The United Nations force in Sierra Leone says it came under attack in the eastern diamond mining town of Kenema over the weekend in one of the most serious incidents since the peace keeping operation began earlier this year.

The UN says it returned fire during the attack by unknown assailants on its headquarters late on Saturday night, and deployed a crack unit of Indian Gurkhas.

A UN spokesman said the Gurkhas got the situation under control but only after an exchange of fire lasting an hour-and-a-half.

The spokesman said earlier reports that the UN had deployed helicopter gunships were untrue and that these reports were caused by confusion among UN officials.

Sources close to the Sierra Leone Government have blamed rebel forces for attacking the UN but it is far from clear on this occasion that the rebels were responsible.

The UN has its largest peace keeping operation in the world in Sierra Leone where it is trying to reconcile various pro-government and rebel forces.

This incident illustrates that despite the peace agreement the situation in Sierra Leone remains complex and extremely dangerous.