LONDON — The oil giant BP faced a new furor on Thursday as it confirmed that it had lobbied the British government to conclude a prisoner-transfer agreement that the Libyan government wanted to secure the release of the only person ever convicted for the 1988 Lockerbie airliner bombing over Scotland, which killed 270 people, 189 of them Americans.
The acknowledgment came after American legislators, grappling with the controversy over the company’s disastrous Gulf of Mexico oil spill, called for an investigation into BP’s actions in the case of the freed man, Abdel Basset Ali al-Megrahi.
After an initial demand for an investigation on Wednesday by four senators from New York and New Jersey, further calls for an inquiry by the Senate Foreign Relations Committee were made on Thursday by Senators Barbara Boxer and Dianne Feinstein, both Democrats of California.
Mr. Megrahi, a former Libyan intelligence agent, was released and allowed to return to Libya in August after doctors advised the Scottish government that he was likely to die within three months of prostate cancer. But nearly a year later, he remains alive and free, though kept out of sight, in Libya’s capital, Tripoli.
BP’s statement on Thursday repeated earlier acknowledgments that it had promoted the transfer agreement to protect a $900 million offshore oil-and-gas exploration deal off Libya’s Mediterranean coast. The British justice minister at the time, Jack Straw, admitted after Mr. Megrahi was repatriated and freed that the BP deal was a consideration in the review of his case.
In the end, Mr. Megrahi was not released under the prisoner transfer agreement. Instead, to the consternation of the Obama administration, and of many of the victims’ families, the Scottish government released him under provisions in Scottish law that allow for a prisoner’s sentence to be commuted on humanitarian grounds, because of Mr. Megrahi’s cancer. That freed him from serving any further prison time in Libya, as he would have had to do under the transfer pact.
American anger over the case found a new outlet this week, with the demands for an investigation of the issue in the United States. On Wednesday, Senators Charles E. Schumer and Kirsten E. Gillibrand of New York, together with Robert Menendez and Frank R. Lautenberg of New Jersey, announced that they had written a letter to Secretary of State Hillary Rodham Clinton asking for a State Department investigation into BP’s role in the prisoner transfer agreement.
Mr. Schumer told reporters that BP should freeze its operations in Libya because it “should not be allowed to profit on this deal at the expense of the victims of terrorism.”
The two California senators, Ms. Boxer and Ms. Feinstein, followed on Thursday with a letter to Senator John Kerry, chairman of the Foreign Relations Committee, declaring that “commercial interests — oil or otherwise — should never be prioritized over justice for victims of terrorist acts and severe punishment for convicted terrorists.”
The Senate Foreign Relations Committee announced Thursday that it would hold a hearing July 29 on Mr. Megrahi’s release and that it would ask BP officials to testify. Mr. Menendez, who will preside over the hearing, said, “For our national security and for fundamental justice, we need answers about the circumstances of this convicted terrorist’s release.”
BP’s business dealings in Libya include an exploration deal in the Gulf of Sidra, which the company estimates could lead to an eventual BP investment of up to $20 billion. The deals represent BP’s return to Libya after decades of exclusion that followed nationalization of the company’s interests there in the 1970s.
BP’s response to the senators’ challenge came in a statement released Thursday, in which BP stuck to its claim that its lobbying was focused on the prisoner transfer pact, not on Mr. Megrahi himself, and that the company had nothing to do with the decision by Scotland to release him.
“It’s not for BP to comment on the decision of the Scottish government,” it said. “BP was not involved in any discussion with the U.K. government or the Scottish government about the release of Mr. al-Megrahi.”
But the company’s critics have said that such a distinction was largely illusory, since Libya’s pressure for the prisoner transfer pact was primarily motivated, as Libyan officials said at the time, by their desire to bring Mr. Megrahi home.
Long before the Gulf of Mexico disaster, the British government’s role in the Megrahi release — and the involvement of British companies with interests in Libya, including BP — had caused deep strains between the Obama administration and the former Labour Party government, which was ousted in May.
The new government responded to the spotlight turned on BP in the affair on Thursday with what amounted to an apology for the former government’s actions. A spokesman for Prime Minister David Cameron said that Mr. Cameron regarded Mr. Megrahi’s release as a mistake, and the British ambassador in Washington, Sir Nigel Sheinwald, said in a letter to Mr. Schumer that the Cameron government “deeply regrets the continuing anguish” the release had caused among the families of Lockerbie victims.
Although senior figures in the Labour government insisted that the Megrahi decision was taken independently by the Scottish government, which has legal powers of its own, an official paper trail showed that officials in London had told Scottish officials, in the context of the prisoner transfer agreement, that letting Mr. Megrahi go would benefit British commercial interests.
That led to widespread suspicions that the Labour government, eager to promote British commercial interests in Libya but reluctant to be seen taking a step — the release of Mr. Megrahi — that would anger Washington, chose to encourage instead an end-around solution that had the Scottish government making the decision.
British officials have noted privately that the last three American administrations have been keen for American oil companies to strike deals with Libya, and that BP has been joined in the contest for potentially lucrative deals by several American oil giants, including Exxon Mobil and Chevron.
Still, the chain of events surrounding Mr. Megrahi fostered deep disillusionment in Washington, where politicians and senior officials criticized what they regarded as Britain’s duplicity in the affair.
Their anger was based, in part, on assurances the United States said it had been given at the time of the Lockerbie trial, held before a Scottish court sitting in the Netherlands, that anybody convicted in the case would serve the full term in Scotland. Mr. Megrahi’s conviction was the only one in the case, after a Libyan accused of being an accomplice, like Mr. Megrahi an agent of Libya’s secret intelligence service, was found not guilty and freed.