Libya expects the United States to remove it from its list of state sponsors of terror now that American companies are returning to Libyan oilfields, a Libyan oil official has said.

Tarek Hassan-Beck, of Libya's National Oil Company, said he was "positive and confident" that the former pariah state would be taken off the list, with the expected backing of the Oasis Group, comprising ConocoPhillips, Marathon and Amerada Hess.

"I would expect logically they will be willing to put the right message across to the US government to do something about it quickly," he said.

An international lawyer who has worked on cases involving Libya said he believed that companies might be reluctant to invest in the country unless they had assurances Washington would restore full ties.

Timothy Scrantom, of Meridian 361 International Law Group, said: "This is a high-risk strategy .... unless of course there were some understanding as to how long the existing sanctions would remain."

Libya's presence on the list bars it from receiving US arms exports, controls sales of items with military and civilian uses, limits US aid and requires Washington to vote against loans from international financial institutions.

A US state department official refused to comment and no one from the Oasis Group was immediately available.