Four UN workers held in Somalia

Mogadishu is controlled by rival armed groups

Negotiations are going on to try to secure the release of four United Nations workers taken hostage in the Somali capital, Mogadishu, on Tuesday.

The four being held are two Britons, a Belgian and a French Algerian.

The United States wants to make clear that the hostage taking is unacceptable

State Department spokesman

They were abducted after gunmen belonging to one of Mogadishu's warlords attacked the offices of a humanitarian organisation.

Five other foreign aid workers - including two Spaniards and a Briton - and a Somali national who were trapped after the gun battle were brought to safety on Wednesday morning.

MSF raid

They were part of a larger group trapped when militiamen belonging to the warlord Musa Sudi Yalahow attacked the Medecins Sans Frontieres offices.

President Abdulkassim Salat Hassan is struggling to impose his authority

All nine were working for a joint UN and WHO programme, vaccinating Somali children against polio.

It is not known whether the gunmen holding the four hostages want ransom money.

The United Nations says it has opened contact with the warlord but it is unclear whether all the hostages are being kept by his gunmen or whether two rival militia groups are now involved.

Foreign aid workers have been targeted before in Mogadishu by gunmen who see them as a lucrative source of foreign currency and negotiations for their release can sometimes be lengthy.

The hostage-taking underlines the problems faced by Somalia's new national government which was formed last year after months of peace negotiations.

The new administration has failed to win over many of the warlords, who regard it as a threat to their powers.

No government

Somalia was without a central government for almost a decade after President Muhammad Siad Barre was ousted in a coup in 1991.

The country was divided into a series of fiefdoms run by warlords and faction leaders.

A peace conference in Djibouti last year established a new central government and appointed Abdulkassim Salat Hassan as president.

The conference, however, was boycotted by many of the faction leaders including Musa Sudi Yalahow.

Those faction leaders have now come together to form the Somali Reconciliation and Restoration Council as a challenge to the government.

US demand

The United States on Tuesday demanded the immediate release of the hostages and said it held the hostage takers responsible for their safety.

"The United States wants to make clear that the hostage taking is unacceptable," US State Department spokesman Richard Boucher said.

Mogadishu is like a tinderbox still with a lot of conflict between factions liable to break out

UN representative in Nairobi

"The hostages should be released at once and the hostage takers in the meantime should remain responsible for ensuring the safety of the people in their custody," he added.

Several Somalis were killed, but all the aid workers were thought to be uninjured following Tuesday's figthing.

In Mogadishu, Abdulkadir Mohammed Mahamud, an aide to Musa Sudi Yalahow, told reporters he had custody of several of the UN staff in a compound belonging to the warlord, saying they had been taken to show the international community Mogadishu was not safe.