LONDON, Sept 25 (Reuters) - A British national has been arrested in Nairobi following the mall siege that killed at least 67 people, the Foreign Office in London said on Wednesday.

According to the Daily Mail newspaper, a 35-year-old Briton of Somali origin was arrested at Nairobi's Jomo Kenyatta airport as he attempted to leave Kenya on a Turkish Airlines flight.

A Foreign Office spokesman declined to comment on the report, saying only that the British authorities were aware of the arrest of a Briton in the Kenyan capital and stood ready to provide consular assistance.

A Kenyan anti-terrorism police unit source also told Reuters that a British citizen of Somali origin was detained after he missed his flight at the Nairobi airport, and was now being questioned. He gave no more details.

The Daily Mail said the man had attracted attention at the airport because he had bruising to his face, was wearing dark glasses and was behaving suspiciously.

The newspaper quoted Kenyan officials as saying the man's British passport appeared to be genuine and it contained a Kenyan visa, although there was no stamp indicating when and how he had entered the country.

The newspaper also said the man said under questioning that his facial injuries happened during a recent visit to Somalia.

Kenya was beginning three days of national mourning on Wednesday for the victims of the siege at the Westgate mall. (Reporting by Estelle Shirbon; editing by Mike Collett-White)

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  • A plume of black smoke billows over the Westgate Mall, in Nairobi, Kenya Monday, Sept. 23, 2013. Multiple large blasts have rocked the mall where a hostage siege is in its third day. Associated Press reporters on the scene heard multiple blasts and a barrage of gunfire. Security forces have been attempting to rescue an unknown number of hostages inside the mall held by al-Qaida-linked terrorists.(AP Photo/Jonathan Kalan)

  • Armed police from the General Service Unit take cover behind a wall during a bout of gunfire, outside the Westgate Mall in Nairobi, Kenya Monday, Sept. 23, 2013. Hostages being held by al-Qaida-linked terrorists in a Nairobi mall have not been released despite an earlier statement from the military that "most" had been rescued, a person connected to the situation told The Associated Press on Monday. (AP Photo/Ben Curtis)

  • Paramedics and police officers run outside the Westgate Mall in Nairobi after heavy shooting started Monday, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff. (AP Photo/Sayyid Azim)

  • Kenya security forces are seen behind a wall outside the Westgate Mall in Nairobi, Kenya Monday morning, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff that killed at least 68 people and injured 175. (AP Photo/Jerome Delay)

  • Kenya security personnel take cover outside the Westgate Mall after shooting started inside the mall early Monday morning, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff that killed at least 68 people and injured 175. (AP Photo/Sayyid Azim)

  • Kenya security forces are seen behind a wall outside the Westgate Mall in Nairobi, Kenya Monday morning, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff that killed at least 68 people and injured 175. (AP Photo/Jerome Delay)

  • Kenya security forces are seen behind a wall outside the Westgate Mall in Nairobi, Kenya Monday morning, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff that killed at least 68 people and injured 175. (AP Photo/Jerome Delay)

  • Onlookers gather on a hill to observe the Westgate Mall after a bout of heavy gunfire just after dawn in Nairobi, Kenya Monday, Sept. 23, 2013. Helicopters circling overhead, Kenya's military launched a major operation Sunday night at the upscale Nairobi mall and claimed it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during a standoff that killed at least 68 people and injured 175. (AP Photo/Ben Curtis)

  • Relatives wait at the Nairobi City Mortuary following the mall attack in Kenya, Sunday, Sept. 22, 2013. Kenyan authorities said Islamic extremist attackers remain inside the upscale Kenyan shopping mall, holding an unknown number of hostages, after killing at least 39 and injuring 150 during Saturday's attack. (AP Photo/Khalil Senosi)

  • Groups of onlookers gather on a road looking down over the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Multiple barrages of gunfire erupted Sunday morning from the upscale Kenyan mall where there is a hostage standoff with Islamic extremists nearly 24 hours after they attacked using grenades and assault rifles. (AP Photo/Ben Curtis)

  • A line of soldiers from the Kenya Defense Forces run in front of the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Multiple barrages of gunfire erupted Sunday morning from the upscale Kenyan mall where there is a hostage standoff with Islamic extremists nearly 24 hours after they attacked using grenades and assault rifles. (AP Photo/Ben Curtis)

  • Soldiers from the Kenya Defense Forces carry a wounded colleague, following the sound of explosions and gunfire, out of the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Associated Press journalists at the scene of a hostage standoff said a barrage of gunfire erupted from the upscale Kenyan mall Sunday morning and moments later two wounded Kenyan security forces were carried out of the mall. (AP Photo/Ben Curtis)

  • Trucks of soldiers from the Kenya Defense Forces arrive after dawn outside the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Islamic extremist gunmen lobbed grenades and fired assault rifles inside Nairobi's top mall Saturday, killing dozens and wounding over a hundred in the attack. Early Sunday morning, 12 hours after the attack began, gunmen remained holed up inside the mall with an unknown number of hostages. (AP Photo/Ben Curtis)

  • Trucks of soldiers from the Kenya Defense Forces arrive after dawn outside the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Islamic extremist gunmen lobbed grenades and fired assault rifles inside Nairobi's top mall Saturday, killing dozens and wounding over a hundred in the attack. Early Sunday morning, 12 hours after the attack began, gunmen remained holed up inside the mall with an unknown number of hostages. (AP Photo/Ben Curtis)

  • Armed special force aim their guns at the Westgate Mall in Nairobi, Kenya on Saturday, Sept. 21 2013, after gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded. A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted(AP Photo/Khalil Senosi)

  • Civilians who had been hiding inside during the gun battle manage to flee from the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013. Gunmen threw grenades and opened fire Saturday, killing at least 22 people in an attack targeting non-Muslims at an upscale mall in Kenya's capital that was hosting a children's day event, a Red Cross official and witnesses said. (AP Photo/Jonathan Kalan)

  • A body is seen on the floor, below right, as smoke fills the air inside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013. Gunmen threw grenades and opened fire Saturday, killing at least 22 people in an attack targeting non-Muslims at an upscale mall in Kenya's capital that was hosting a children's day event, a Red Cross official and witnesses said. (AP Photo/Jonathan Kalan)

  • A woman who had been hiding during the gun battle runs for cover after armed police, seen behind, enter the Westgate Mall in Nairobi, Kenya, Saturday, Sept. 21, 2013. Gunmen threw grenades and opened fire Saturday, killing at least 22 people in an attack targeting non-Muslims at an upscale mall in Kenya's capital that was hosting a children's day event, a Red Cross official and witnesses said. (AP Photo/Jonathan Kalan)

  • An armed police officer takes cover during a bout of gunfire outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013. Gunmen threw grenades and opened fire Saturday killing at least 22 people in an attack targeting non-Muslims at an upscale mall in Kenya's capital that was hosting a children's day event, a Red Cross official and witnesses said. (AP Photo/Ben Curtis)

  • People run from the Westgate Mall in Nairobi, Kenya.

    Gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded. A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted.

  • A woman who had been held hostage reacts after being released.

    Suspected terrorists engaged Kenyan security forces in a drawn out gun fight at the Westgate Mall in Nairboi.

  • Woman runs for cover.

    A woman who had been hiding during the gun battle runs for cover after armed police, seen behind, enter the Westgate Mall in Nairobi, Kenya, Saturday, Sept. 21, 2013.

  • Location of the attack.

    Graphic shows detail of shopping mall site of fatal gun attack in Nairobi, Kenya.

  • View inside the mall.

    Armed police take cover behind escalators as smoke fills the air inside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • Raw: Gunmen Attack Shopping Mall in Kenya

    Gunmen threw grenades and opened fire at an upscale mall in Kenya's capital on Saturday, killing at least 10 people.

  • Armed police on scene.

    Armed police leave after entering the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • Mall-goers flee after attack.

    Civilians who had been hiding inside during the gun battle manage to flee from the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • An armed police officer takes cover during a bout of gunfire outside the Westgate Mall.

    The mall in Kenya's capital was hosting a children's day event at the time of the attack, a Red Cross official and witnesses said.

  • Armed police at the Westgate Mall.

    Armed police crouch down and take position during a gun battle outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • Civilians leave the mall after gun battle.

    Civilians who had been hiding during the gun battle hold their hands in the air as a precautionary measure before being searched by armed police leading them to safety, inside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • A rescue worker helps a child outside the Westgate Mall.

  • Security helps a woman outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013, after gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded.

  • People flee the scene of the attack.

    Security helps people outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013, after gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded.

  • A wounded man is escorted away from the mall.

    Witnesses say a half dozen grenades also went off along with volleys of gunfire in and around the mall.

  • A rescued hostage collapses on the ground after being freed by police at Westgate Mall.

    A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted.

  • Two women hug outside the mall after the attack.

    Bursts of gunfire were heard from outside the Westgate Mall Saturday, where cars were left abandoned. Witnesses say a half dozen grenades also went off along with lobbies of gunfire that started at midday.

  • Woman escapes from the Westgate Mall.

    A woman who had been hiding inside and managed to flee, sits in a state of shock, as an unidentified armed member of the security forces, above, keeps watch outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • Security officers keep a crowd under control outside the Westgate Mall

  • An injured person makes a phone call as he is helped on his arrival at the Aga Khan Hospital after the attack at the Westgate Mall.

  • An injured person arrives at the hospital after the attack on the Westgate Mall.

  • A injured child is wheeled away on a shopping trolley outside the Westgate Mall.

  • A security officer helps a wounded woman outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013, after gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded. A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted. (AP Photo/Khalil Senosi)

  • An injured man arrives at the Aga Khan Hospital in Nairobi after the attack at the Westgate Mall.

  • An injured man arrives at the Aga Khan Hospital after the attack at the Westgate Mall.

    A witness to the attacks says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted. Initial police reports had described the incident as a botched robbery. Witnesses say a half dozen grenades also went off along with volleys of gunfire in and around the mall.

  • A security guard helps a child outside the Westgate Mall.

    A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted.