The Embassy of the United States in Sri Lankan capital Colombo was closed early on Tuesday on account of a security threat, diplomatic sources said.

The embassy closed its offices at 2:00 p.m. local time and details of the threat were not immediately known.

Sources said that the USAID (United States Agency for International Development) office and the US information service center, located on the same avenue on the high security zone in the western part of the capital, were also closed at the same time.

The Sri Lankan prime minister's office and British and Indian diplomatic offices are also located within close proximity to the US embassy.

But both missions are carrying on business as usual, the sources added.

Early last month a Tamil Tiger rebel suicide attack inside the police station opposite the US embassy killed four policemen and the suicide bomber herself and injured 12 people.

It was the first explosion in the city since February 2002 when the Tamil Tiger rebels and the government entered the ongoing ceasefire.