By Mohammed Ghobari and Lara Sukhtian
SANAA/GENEVA, June 17 (Reuters) - Car bombs killed or injured at least 50 people near mosques and the headquarters of Yemen's dominant Houthi group in Sanaa on Wednesday, in coordinated attacks claimed by Islamic State.
The four blasts rocked the capital as Saudi-led forces conducted more air strikes against Houthi military bases across Yemen and Houthi delegates attending peace talks in Switzerland reported the first tentative progress on the second day of a U.N.-sponsored push for a Ramadan truce.
A security official said at least 50 people were killed or wounded in the attacks on the Hashush mosque, the Kibsi mosque, the al-Qubah al-Khadra mosque and the political bureau of the Ansarullah movement of the Houthis, who belong to the Zaydi sect of Shi'ite Islam.
"The explosion was so loud I thought it was caused by an air strike," said a man in his 70s named Ali, who had just left a mosque when a bomb went off.
"I returned and found cars burning, people screaming and wounded people all over."
The Sunni Muslim Islamic State said in a statement posted online it carried out the attacks.
"The soldiers of the Islamic State in Yemen, in a wave of military operations as revenge for the Muslims against the Houthi apostates, (detonated) four car bombs near the centers of Houthi apostasy," it said.
The attack is the most serious of its kind in Yemen since suicide bombers killed at least 137 worshippers and wounded hundreds during Friday prayers at two mosques in Sanaa on March 20, in attacks also claimed by Islamic State.
The Houthi-controlled state news agency quoted an official blaming Islamic State for the latest bombings. Supporters of Islamic State exchanged celebratory messages on social media.
Islamic State has recently stepped up its operations in Yemen, where Al Qaeda in the Arabian Peninsula (AQAP), also Sunni Islamist, had long dominated the militant scene.
AQAP recently suffered a serious blow when a U.S. drone strike killed its leader, Nasser al-Wuhayshi.
Earlier on Wednesday Houthi fighters in central Yemen blew up the home of a senior politician, Abdel-Aziz Jubari, while he was attending the Geneva talks as a member of the exiled government's delegation.
Yemen's Foreign Minister Reyad Yassin Abdulla told Reuters in Geneva the peace talks had "made no progress."
Residents of Dhamar city said the Houthis, who had taken over Jubari's house in April, dynamited the building early in the morning. Yemeni websites published pictures of its collapsed roof on a pile of rubble.
Jubari, who is deputy head of the delegation sent to Geneva by ousted President Abd-Rabbu Mansour Hadi, said he was shocked when he heard the news.
"Of course my house is not the only house in Yemen," he told Reuters in Geneva. "A lot of people's homes and properties have been targeted in an unbelievable way."
Abdulla, the head of the government delegation, said: "It is in this spirit of revenge that they are dealing with all the Yemeni people and we cannot remain silent on this."
Houthi officials were not immediately available to comment on the incident.
The Houthis seized Sanaa in September and pressed into the country's center and south, forcing Hadi and his government into exile in Riyadh.
They say they are campaigning against corruption and years of political marginalization.
A coalition of Arab states headed by Saudi Arabia has been bombing the Houthis and their Yemeni army allies since March 26.
Their aim is to restore Hadi to power and head off what they see as Shi'ite Iran's expansion in the region. The Houthis deny receiving military backing from Iran.
More than 2,600 civilians and combatants have been killed since March and a humanitarian crisis is looming as supplies of food, medicine and other goods run short.
CEASEFIRE CHANCES DAMPENED
In Geneva, the U.N's special envoy to Yemen, Ismail Ould Cheikh Ahmed, has been conducting shuttle diplomacy between the two sides.
Early on Wednesday Abdulla played down the prospects of a quick ceasefire deal, saying his team still wanted the implementation of a U.N. Security Council resolution demanding the Houthis quit cities they have seized since September. He said he did not want a truce merely "for the sake of publicity."
U.N. envoy Ould Cheikh Ahmed said he remained optimistic. But Abdulla said the Houthis had not formed their negotiating team by early evening.
Hours later, after meeting the U.N. envoy, Hamza Al Houthi who leads Houthi delegation, told reporters talks would continue on Thursday. "There is progress on some ideas and issues."
Houthi delegate Ali Imad said: "There was greater openness and acceptance from the U.N. envoy. All these are signs that today we are moving towards building the first step to resolving this crisis." (Additional reporting by Tom Miles in Geneva, Ahmed Tolba in Cairo and Mohammed Mukhashaf in Aden; Writing by Sami Aboudi; Editing by William Maclean and Ralph Boulton)