Senators postponed a hearing on whether British oil giant BP Plc influenced the release of the Lockerbie bomber, saying on Tuesday key witnesses had stonewalled the investigation by refusing to appear.

Senator Robert Menendez announced the postponement of the Senate Foreign Relations Committee hearing set for Thursday and said it would be rescheduled in the near future.

U.S. anger over the BP oil spill in the Gulf of Mexico has renewed interest in the details of last year's release by Scottish authorities of Libyan intelligence officer Abdel Basset al-Megrahi, who was convicted of the 1988 bombing of Pan Am flight 103 over Lockerbie, Scotland.

Most of the 270 people killed were Americans. The Senate panel wants to know if BP had influence in the bomber's release as it pursued business interests in Libya.

Menendez said the Senate committee had called two Scottish officials, former British Justice Secretary Jack Straw and two BP executives -- including departing chief executive Tony Hayward -- but all had declined to testify.

It is utterly disappointing and I think pretty outrageous that none of these key witnesses will cooperate with our request to answer questions before the Senate Foreign Relations Committee. They have stonewalled, Menendez told reporters.

It is a game of diplomatic tennis that is worthy of Wimbledon but not worthy on behalf of the lives of the families who still have to deal with this terrorist act and the consequences of the lost loved ones.

He said the panel would conduct a longer-term investigation of the release of the Lockerbie bomber, noting the Scottish government did offer to provide answers to further questions.

We appreciate that and we will take them up on their offer, he said.

As a rule, Senate panels cannot subpoena foreign nationals to compel them to appear, Menendez said. But the committee was examining whether it could use subpoena power in the case of a British citizen like Hayward because he is part of a company doing business in the United States.

BP has offered to send another representative, the head of the company's UK operations, Peter Mather, an aide to Menendez said earlier. But the aide said there was no indication Mather had been in communication with Libya about the 2007 exploration and production deal BP signed with Tripoli.

The Scottish government has denied it had any contact with BP before deciding to free the Lockerbie bomber last year.

BP has said it had expressed concerns and lobbied the British government about the slow progress in resolving a different prisoner transfer agreement with Libya in 2007.

(Editing by John O'Callaghan)