Yemeni forces ended a hostage crisis on Monday with 29 police and six civilians dead, a day after the attack claimed by the militant Islamic State group began with suicide bombings, official sources said.

Assailants on Sunday stormed the criminal investigations unit in Aden, the Yemeni government's de facto capital, setting it alight and taking hostages after killing two policewomen.

The attack began on Sunday, when two suicide bombers blew themselves up at the entrances to the criminal investigations unit and the city's security headquarters.

Overnight, the security forces tried three times to seize back the unit, but each time a suicide bomber blew himself up, stopping them from entering, a security official said.

A fourth suicide bombing occurred on Monday morning, before the security forces finally brought an end to the standoff in the southern port city.

A total of 29 members of the security forces were killed during the attack and hostage crisis, the official said.

Among them were six police officers whose bodies were found buried under the rubble of the building along with six civilians, including two children.

“The security forces have managed to enter the building and clear it of the elements of evil and terrorism,” said the interior ministry of President Abedrabbo Mansour Hadi's internationally recognised government.

The bullet-riddled bodies of three assailants were also found in the rubble, the security official said.

The attack was claimed by IS in a statement released online on Sunday.

IS and its extremist rival Al Qaeda have taken advantage of the war between the Saudi-backed government and Huthi rebels allied with Iran to bolster their presence across much of south Yemen.

The Hadi government has been based in Aden since the Huthis drove it out of the capital Sanaa in 2014.

More than 8,650 people have been killed in Yemen since Saudi Arabia and its allies joined the war in 2015 to support government forces, according to the World Health Organisation.