SANAA (AFP) - Multiple suicide bombings claimed by the Islamic State in Iraq and Syria (ISIS) group killed at least 142 people Friday at Shi'ite mosques in Yemen's capital - one of the strife-torn country's deadliest ever militant attacks.

The killings were the first claimed by ISIS in Yemen and represent a strong show of force by the group in a country where rival Al-Qaeda is the most prominent militant organisation.

Charred bodies and pools of blood were seen at the scene of the blasts, which targeted supporters of the Huthi Shi'ite militia that has seized control of the capital Sanaa.

Worshippers rushed the wounded to hospitals in pick-up trucks, while others evacuated mutilated bodies.

One suicide bomber struck inside Badr mosque in southern Sanaa while another targeted worshippers as they fled outside, witnesses said.

A third suicide bomber targeted Al-Hashush mosque in northern Sanaa, while a fourth struck outside the mosque, according to the Saba news agency, which is now controlled by the Huthis.

Nashwan al-Atab, a member of the health ministry's operations committee, told AFP that 142 people were killed and at least 351 were wounded.

Huthi TV said hospitals had made urgent appeals for blood donations.

The imam of the Badr mosque was among the dead, a medical source said.

Another suicide bomber blew himself up outside a mosque in the northern Huthi stronghold of Saada, a source close to the militia said.

Only the assailant was killed in that explosion, and tight security at the mosque prevented the bomber from going inside, the source added.

'TIP OF THE ICEBERG'

In an online statement, the Sanaa branch of ISIS said the attacks were "just the tip of the iceberg".

"Infidel Huthis should know that the soldiers of the Islamic State will not rest until they eradicate them... and cut off the arm of the Safavid (Iranian) plan in Yemen," the statement said.

The Huthis are accused of receiving support from Iran.

ISIS, a radical Sunni Muslim organisation, considers Shi'ites to be heretics.

Al-Qaeda in the Arabian Peninsula issued a statement saying it had nothing to do with the bombings.

"We stress that we abide by the instructions of Sheikh Ayman Zawahiri, to avoid targeting mosques and markets... to protect the lives of innocent Muslims," it said.

The Huthis overran Sanaa in September and have since tightened their grip on power.

Their attempts to extend their control into other areas have been met by deadly resistance from Sunni tribes and Al-Qaeda, which is the target of a long-standing US drone strike campaign.

The United States condemned the mosque bombings but said it could not confirm the voracity of the ISIS claim of responsibility.

"We deplore the brutality of the terrorists who perpetrated today's unprovoked attack on Yemeni citizens, who were peacefully engaged in Friday prayers," White House spokesman Josh Earnest said.

But there is not, as yet, a "clear operational" link between Yemeni extremists and the Islamic State in Syria and Iraq, he added.

Yemen has descended into chaos since the 2012 ouster of longtime strongman Ali Abdullah Saleh, who has been accused of backing the Huthis.

Friday's blasts came a day after clashes between forces loyal to President Abedrabbo Mansour Hadi and those allied with the Huthis in the southern city of Aden.

Since fleeing to Aden last month, President Hadi has been struggling to reassert his authority, and violence has erupted there in recent days between forces loyal to him and to the Huthis.

A security official said Friday a top Yemeni officer linked to the Huthis had escaped an assassination bid near Aden overnight.

Four people were killed in an ambush on the Lahj-Taiz road, but General Abdel Hafedh al-Sakkaf, the special forces chief in Aden, escaped unharmed, said the official from Lahj.

The attack came as Hadi loyalists tightened their control over Aden, where the situation was calm early Friday.

Hadi had to evacuate a presidential palace in Aden on Thursday after a fighter jet opened fire, hitting a nearby hill.

Separately, 11 people were killed Thursday when special forces fighters loyal to the Huthis tried to seize control of Aden's airport from Hadi loyalists, in fighting that forced its closure.

The airport reopened Friday with a flight to Sanaa.

Following the Huthi takeover of Sanaa, Saudi Arabia and other Gulf countries moved their embassies to Aden and several Western missions closed their doors in the capital for security reasons.

In other unrest, five people - three gunmen and two policemen - were killed as southern separatists attacked police centres in Lahj, a security official said.