U.S. President Barack Obama has announced sanctions against the Libyan government, blocking transactions involving assets of Col Gaddafi and several of his close associates.

Obama signed an executive order freezing the assets of Colonel Gaddafi and members of his immediate family. The White House said the move aimed to pressure Libya to stop violently repressing the popular uprising there.

A spokesman said it was made "in concert with international partners".

"The Libyan government's continued violation of human rights, brutalization of its people, and outrageous threats have rightly drawn the strong and broad condemnation of the international community," Obama said in a statement. "These sanctions therefore target the Gaddafi government, while protecting the assets that belong to the people of Libya."

Earlier, at a hastily organized news conference at the UN in New York, Libyan deputy ambassador Ibrahim Dabbashi described Col Gaddafi, who has been in power for 42 years, as a "madman".

He warned that thousands would die in Tripoli because the Libyan leader would never flee and would fight to the end, BBC reports.