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Earlier, US officials said they believed a Somali-based Islamic group - Al-Ittihad al-Islamiya (AIAI), also known as the Islamic Union - may have carried out Thursday's attacks against Israeli targets in the Kenyan city of Mombasa.

Kenyan authorities are continuing to question 10 people detained in connection with the attacks, after two Westerners were cleared of involvement and released from police custody on Saturday.

No link has been established between those detained and the al-Qaeda terror network, which is also suspected of carrying out the attacks on the Israeli-owned Paradise Hotel, near Mombasa, and an Israeli aircraft, Kenyan authorities said.

Terror alert

The State Department said it had not yet verified the information that more terror attacks might take place, but that US citizens should carefully consider whether to travel to, or stay in, east Africa.

Since the 11 September terrorist attacks, the US has stepped up its military and diplomatic involvement in the area.

In a separate statement, the State Department repeated a warning to US nationals not to travel to Yemen, which lies across the Red Sea from Djibouti.

"The department has received credible reports that terrorists associated with al-Qaeda have planned attacks against US interests in Yemen and... anticipates that threats against American citizens in Yemen will continue," the statement said.

On Saturday, workers at the Paradise Hotel in Kikambala, returned to the burnt-out resort for a special prayer service for the victims of the attack.

As police hunted for clues, Kenyan Government minister Katana Ngala urged Kenyan Muslims to come forward with information.

"This is not a witch-hunt. We want to get the culprits and punish them," he told those at the service.

Suspects questioned

Kenyan authorities say they have detained six Pakistanis and four Somalis in connection with the attacks.

Pakistani diplomats have complained that they have not been given consular access to suspects claiming Pakistani nationality.

The Pakistani High Commissioner in Kenya, Hamid Asghar Quidvai, told the BBC it was unclear whether the men were Pakistanis because their documents were issued in the Somalian capital Mogadishu - where there has been no Pakistani high commission for 10 years.

A young couple from Florida, who were arrested after checking out of a nearby hotel shortly after the explosion, were questioned for two days before being released.

Emerging from a police station, American Alicia Kalhammer and her Spanish husband, Jose Tena pair said they bore no grudges.

"There are no hard feelings. We love Kenya," said 31-year-old Alicia.

Troublesome border

As the investigation into the Kenya attacks continued, US officials said they suspected the involvement of the AIAI, a prominent militant organisation in the Horn of Africa with links to the al-Qaeda network.

Somali cleric Sheikh Ali Sheikh Mahmud, who has been linked to the group, said he was "very sorry" about the attack in Kenya, but added that "no-one can ignore the rights of Muslims in this world," Reuters news agency reported.

AIAI is thought to have been behind bomb attacks in the Ethiopian capital Addis Ababa in 1996 and 1997 and the kidnapping of relief workers in 1998.

Kenya has a long remote border with Somalia which is particularly difficult to police because of incursions by armed bands known as shiftas.

Ten years of conflict and instability in Somalia have made weapons easily available in border areas.