SANAA (AFP/Reuters) - An explosion rocked a mosque in Yemen's rebel-held capital on Thursday (Sept 24) during prayers for the Muslim holiday of Eid al-Adha, witnesses said, killing at least 25 people.

The blast, reportedly triggered by two suicide bombers, happened in the Blili mosque near a police academy in Sanaa, which is controlled by the Huthi Shi'ite insurgents, according to witnesses.

Medics said at least 25 people were killed and dozens more were wounded.

Witnesses reported that after a first blast inside the mosque, a suicide bomber detonated an explosives belt at the entrance as worshippers rushed outside.

It was not immediately clear if the first blast was also from a suicide bomber.

The bombing came as Muslims around the world celebrated the Eid al-Adha - the feast of sacrifice - which Muslims mark by prayers in congregation at mosques.

No group immediately claimed responsibility for the attack.

The Yemeni capital has been shaken by a string of bombings of Shi'ite mosques in recent months claimed by the Islamic State in Iraq and Syria (ISIS) group.

The radical Sunni Muslim group considers Shi'ites to be heretics and has also claimed bombings of mosques in Kuwait and Saudi Arabia.

The Iran-backed Huthi rebels have seized several regions of Yemen including Sanaa which they overran a year ago.

Pro-government forces backed by Saudi-led air strikes have recently managed to wrest back some southern provinces, including Yemen's second city of Aden.

ISIS group and the Yemen-based branch of its rival Al-Qaeda have exploited the turmoil to boost their activities in the impoverished country.

After six months in exile in neighbouring Saudi Arabia, President Abedrabbo Mansour Hadi returned to Aden on Tuesday with a vow to liberate the country from the Huthis. The Saudi-led coalition launched air strikes against the rebels on March 26, and began a ground operation in July.

Hadi loyalists began an all-out offensive against the Huthis in the oil-rich Marib province east of Sanaa earlier this month, aiming to retake the capital.

The United Nations says around 5,000 people have been killed and 25,000 wounded, many of them civilians, since late March in Yemen.

Yemen has descended into chaos since the 2012 ouster of longtime strongman Ali Abdullah Saleh, and security has broken down since Huthi militiamen swept unopposed into the capital a year ago.

Al-Qaeda has long been the dominant militant force in Yemen, located next to oil-flush Saudi Arabia and key shipping lanes, but experts say ISIS is seeking to supplant its extremist rival. Al-Qaeda in the Arabian Peninsula (AQAP) controls parts of the vast southeastern province of Hadramawt, including the provincial capital Mukalla, which it is seized in April.

It has distanced itself from ISIS' tactics, saying that it avoids targeting mosques to protect "innocent Muslims".

The United States has waged a longstanding drone war against AQAP which it regards as the militant network's most dangerous branch.