But Cameron says the decision was not made by BP, "but by the Scottish government." Cameron spoke at a joint news conference Tuesday with President Barack Obama.
Cameron urged American to avoid confusing "the oil spill with the Libyan bomber."
Cameron also said he understood American anger over the BP oil spill in the Gulf of Mexico.
He said the spill that began April 20 with an explosion aboard a BP-leased oil rig that claimed 11 lives was "a catastrophe" for the environment, the fishing industry and for tourism in the region.
Cameron said he agreed with Obama that "it is BP's role to cap the leak, clean up the mess and pay the appropriate compensation." He said that the recent temporary capping of the well by BP was "a step in the right direction."
At the same time, Cameron said that BP, formerly known as British Petroleum, "is an important company to both" the United States and Britain, noting it employs thousands of workers on both sides of the Atlantic.
It was the British prime minister's first visit to the United States since taking office ten weeks ago. However, he and Obama met one-on-one last month on the sidelines of a world summit in Toronto and discussed some of the same issues.
CBSNews.com Special Report: Disaster in the Gulf
There was one item on which the two leaders basically agreed to disagree, however: the vastly different approaches to budget-cutting the two countries are taking amid a fragile economic recovery.
Cameron's coalition government has imposed stringent spending cuts, while the Obama administration favors eventual deficit reduction -- but does not want to slam on the stimulus brakes too quickly for fear of jeopardizing a fragile recovery and plunging the U.S. back into recession.
Obama said there would be differences in how different countries "approach it tactically and at what pace."
He also said there was "no closer ally and no closer partner" than Britain. He reaffirmed the "truly special relationship" between the two nations.
"We speak a common language, most of the time," Obama joked.
A key item of their private discussion was Afghanistan, where Britain has the most troops serving of any NATO nation after the United States. But Cameron has said he wants his country's 10,000 troops out by the time of Britain's next election, which must be held by 2015.
The prime minister participated in a working lunch with Obama and Vice President Joe Biden, whom he met earlier for breakfast at the British Embassy.
Cameron had hoped to use his first official visit to the White House to build his standing as a statesman and develop his relationship with Obama. Instead, he was forced to focus on the British government's decision last August to return the cancer-stricken prisoner to Libya on compassionate grounds.
Al-Megrahi served eight years of a life sentence for the Dec. 21, 1988, bombing of Pan Am Flight 103 as it flew over Lockerbie, Scotland, en route to New York. The bombing killed 270 people, almost all of them Americans. He was released and returned to Libya in August 2009 after doctors said he had only three months to live, but a doctor now says he could live for another decade.
Cameron said that, while Scotland is part of Britain, Scotland had the authority to make the release decision under the limited powers it has on its own -- and that the British government of his predecessor, Gordon Brown, did not participate in the decision.
Cameron will meet Tuesday evening with U.S. lawmakers who have urged an inquiry into BP's alleged lobbying of the British government over al-Megrahi's release.
Libya's proven oil reserves are the ninth-largest in the world, but vast areas remain unexplored. The country has been working to bring in foreign oil companies and investors after U.S. and U.N. sanctions were lifted several years ago.
The U.S. lawmakers asked the State Department last week to investigate whether BP pressured officials as part of efforts to seek access to Libyan oil fields.
Cameron was to complete his two-day visit on Wednesday in New York, with meetings with United Nations Secretary-General Ban Ki-moon and New York Mayor Michael Bloomberg.