Mr Obama outlined a range of possible measures, including plans for humanitarian assistance.

Earlier, Mr Obama telephoned French President Nicolas Sarkozy of France, UK Prime Minister David Cameron and Italian Prime Minister Silvio Berlusconi to co-ordinate a response to the Libya crisis.

"The president expressed his deep concern with the Libyan government's use of violence which violates international norms and every standard of human decency," said a statement.

"The leaders discussed the range of options... to hold the Libyan government accountable for its actions, as well as planning for humanitarian assistance."

US officials said the steps could include seeking stronger action by the UN Security Council - including possible sanctions such as travel bans and asset freezes - support for calls to suspend Libya from the UN Human Rights Council, and enforcing a no-fly zone over Libya.

The UN Security Council is expected to meet later on Friday in New York to consider further action against Col Gaddafi's government.

US Secretary of State Hillary Clinton is due to travel to Geneva on Monday for a meeting of the UN Human Rights Council focusing on Libya.

The Swiss government has ordered an immediate freeze on assets belonging to Col Gaddafi and his associates.