BBC News with Iain Purdon

President Obama has again demanded that the

embattle

d Libyan leader Muammar Gaddafi

step down

. Mr Obama repeatedly told a White House news conference that Colonel Gaddafi had lost the

legitimacy

to lead. He warns that those responsible for violence against civilians will be held accountable. With more, here's Kim Ghattas in Washington.

It's not the first time that Barack Obama has called on the Libyan leader Muammar Gaddafi to leave office.

Last week, the White House put it in a written statement. This time, Mr Obama did it in a televised press conference. It's part of the slow but steady

ramping up

of the pressure on Mr Gaddafi. Mr Obama also said he had

instruct

ed the Department of Defence and the State Department to examine a full range of options so that the United States could act rapidly if the situation deter

iorate

d.

The International Organisation for Migration says 200,000 migrant workers have now left Libya, crossing into Egypt, Tunisia and Niger. An international airlift has been organised. Jeremy Bowen sent this report from a Libyan border crossing into Tunisia.

Without the foreign workers on whom this country's economy relies, Libya is feeling even more isolated. The good news for Colonel Gaddafi is that the road from here, the Tunisian border, back to Tripoli is under his control, except for the centre of one town, Zawiya. The bad news is that his security services don't know who they can trust here in western Libya. They are still raiding houses at night and taking people away. The colonel does have