"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 centres of Houthi apostasy," a statement from the IS group read.

Yemen's conflict pits the Houthis - who seized the capital last year - and military units loyal to former President Ali Abdullah Saleh against an array of forces, including southern separatists, local and tribal militias, Islamic militants and loyalists of exiled President Abed Rabbo Mansour Hadi. The Saudi-led coalition backing Hadi began carrying out airstrikes in March.

The Arab world's poorest nation is also home to the world's most dangerous al-Qaida offshoot. The group, whose leader was killed in a US drone strike last week, has targeted the Houthis in dozens of deadly attacks, and its militants are engaged in daily attacks in central Yemen.

UN-brokered talks between the rival factions are underway in Geneva, aimed at ending the violence and addressing the humanitarian crisis in Yemen. Mediators hope for a humanitarian truce during Ramadan, which starts Thursday, but neither side has shown any desire to compromise.

The earlier Saudi-led airstrikes struck a convoy of civilian vehicles fleeing north from the southern city of Aden, which has seen intense fighting. Medics described a scene of carnage, with body parts scattered across the highway and smoke billowing from charred vehicles. They said at least 31 people had been killed.

Despite nearly three months of airstrikes, anti-Houthi forces have made little progress. The violence has killed nearly 1500 civilians and injured over 3000 others, according to the UN.

Violent clashes

Heavy fighting was also reported in the Marib province east of the capital, Sanaa, where Sunni tribes have fended off a number of Houthi advances on the city of al-Saheel, security officials said. Airstrikes targeted the Houthis in Marib as well as in Sanaa, the rebels' northern heartland and the western city of Taiz, they said.

In a country already suffering from shortages of fuel, water and medical supplies, the fighting endangers hospitals as well. A report released Wednesday by Human Rights Watch accused the Houthis and their rivals of turning a main hospital in Aden into a warzone.

In one incident in mid April, the group said hundreds of southern fighters forced staffers to relocate injured Houthis receiving treatment there. Human Rights Watch says at least two of the wounded were shot dead outside the hospital.

glb/bw (Reuters, AFP)