The United States would "encourage" any new Libyan government to help a new investigation of the 1988 bombing of Pan Am Flight 103 over Lockerbie, Scotland, a top US official said.

"I would encourage them, we would hope that they would do that," Deputy US Secretary of State James Steinberg told Democratic Senator Robert Menendez during a hearing of the Senate Foreign Relations Committee on Libya.

But Steinberg repeatedly sidestepped Menendez's push to make US diplomatic recognition of any government to replace embattled strongman Moamer Kadhafi contingent on cooperating on a new probe into the attack.

"We share the importance that you attach to it," the diplomat said, but it would be better for Libya to do so of their own accord "rather than because we impose the commitment."

Menendez said he had met with senior Libyan opposition figure Mahmud Jibril, who handles foreign policy for Libya's National Transitional Council (NTC) and discussed the issue.

"He indicated that, once a new government is formed, that they would be willing to cooperate with the United States on a new investigation" into the Lockerbie bombing, said the senator.

"We certainly welcome the offer that he made. We think it would be important in terms of long-term relations," said Steinberg.

Libyan agent Abdelbaset Ali Mohmet al-Megrahi is the only man convicted over the bombing of Pan Am flight 103 over the Scottish town of Lockerbie in December 1988, which killed 270 people, most of them US nationals.

Megrahi, who has terminal cancer, was released from a Scottish jail on compassionate grounds in August 2009.

Scottish prosecutors, who as part of a devolved administration operate independently from the British government in London, have said that they are still investigating the bombing.