ADEN/SANAA, July 24 (Reuters) - A booby-trapped car drove into an army checkpoint outside of Yemen's southern port city of Aden and exploded in an apparent suicide attack that killed at least six people and injured 15 on Sunday, police and medical sources said.
The army has strengthened security around the coastal city to try to stop Islamist militants from slipping into the area after they seized several areas in the neighbouring province of Abyan during months of protests to try to oust the president.
Aden lies east of a shipping strait, where some 3 million barrels of oil pass daily.
"The initial evidence we've gathered suggests it was a suicide bomb attack," a local police source told Reuters.
The blast comes days after a car rigged with explosives blew up and killed a British ship surveyor in Aden, which officials said was a targeted attack against the long-time resident.
Witnesses to the checkpoint attack on Sunday said they saw a car speed into a street cordoned off by armoured vehicles, setting at least two armoured vehicles ablaze.
"The car crashed into a military armoured vehicle, which exploded and caught fire. The soldiers started firing heavily," a witness said.
Security forces sealed off the al-Harba area of Aden and witnesses said they could still hear heavy gunfire.
Aden sits to the west of the flashpoint province of Abyan, which has descended into daily bloodshed since militants seized at least two cities and a makeshift military base, forcing some 54,000 residents to flee to Aden for refuge.
The army has staged a fierce offensive against the militants, who they say are linked to al Qaeda, but has yet to regain control of those areas.
One security source said the vehicles targeted in the Sunday attack were part of a convoy of forces being sent to join the military operation in Abyan, which has lasted for more than a week.
The unrest in the south has erupted during the mass protests seeking to end President Ali Abdullah Saleh's 33-year rule. Saleh is convalescing in Riyadh after a bomb blast in his presidential compound in June.
The United States and neighbouring oil giant Saudi Arabia, both targets of failed attacks by al Qaeda's Yemen-based wing, fear rising turmoil in the Arabian Peninsula state may give the militant group more room operate. (Reporting by Mohammed Ghobari; Writing by Erika Solomon)
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