Despite the strong words, the diplomatic end of the decades-long Lockerbie saga is unlikely to damage steadily warming relations between the West and Libya, a country once reviled as a pariah state.
"It will introduce a note of caution in the West's dealing with Libya," said Diederik Vandewalle, a Libya specialist at Dartmouth College in New Hampshire. "I don't think it will have much of an impact at all."
Thousands of young men greeted al-Megrahi's plane at a Tripoli airport after he was released from a Scottish prison Thursday on compassionate grounds. Some threw flower petals as the 57-year-old former Libyan intelligence agent stepped from the jet.
British Foreign Secretary David Miliband condemned the scenes as "deeply distressing," and said the way Moammar Gadhafi's government behaved in the next few days would help determine whether Libya is accepted back into the international fold.
Prime Minister Gordon Brown had written to the Libyan leader before al-Megrahi's release urging Libya to "act with sensitivity" when he returned.
White House spokesman Robert Gibbs said footage of al-Megrahi's arrival was "tremendously offensive to the survivors that, as I said, lost a loved one in 1988."
"I think the images that we saw in Libya yesterday were outrageous and disgusting. We continue to express our condolences to the families that lost a loved one as a result of this terrorist murder," he told reporters.
Gibbs said the White House had been in contact with Libyan authorities. "We've registered our outrage. We have discussed with the Libyans about what we think is appropriate. We'll continue to watch the actions of this individual and the Libyan government."
Yet by Libyan standards, al-Megrahi's welcome was relatively muted. Hundreds of people waiting in the crowd for his plane were rushed away by authorities at the last minute, and the arrival was not aired live on state TV.
It was an unusually low-key approach for a country that used to snap up any opportunity to snub the West and could easily bring out hundreds of thousands to cheer if it chose to. It suggested that Libya is wary of hurting its ties with the U.S. and Europe and had listened to Obama's warning not to give al-Megrahi a hero's welcome.
"It seemed as some form of last-minute compromise between those who felt it their patriotic duty to welcome him and those in the Libyan hierarchy who wanted to heed the demands of the U.S. that it should be low-key," said Richard Dalton, a former British ambassador to Libya.
"There was no Libyan dignitary to receive him, and no formal reception. This is compulsory in Arab hospitality, so the absence of a welcoming party is quite significant," he added.
Al-Megrahi is the only man convicted in the bombing of Pan Am Flight 103 over Lockerbie, Scotland. The explosion of a bomb hidden in the cargo hold killed all 259 people on the plane and 11 on the ground in Britain's worst terrorist attack.
Libya and Britain have acted to make al-Megrahi's release as smooth and understated as possible.
Announcing it Thursday, Scottish Justice Secretary Kenny MacAskill said he was acutely aware of the bereaved families' pain, and stressed that he had made the decision only on narrow legal grounds. Cancer specialists have given al-Megrahi less than three months to live, and it is established legal practice to release prisoners that close to death on compassionate grounds.
There have been 30 requests for compassionate release in Scotland over the last decade, 23 of which were approved. Al-Megrahi also was released just in time to arrive home for the start of the Muslim holiday of Ramadan.
MacAskill said while "those who have been bereaved cannot be expected to forget, let alone forgive ... Mr. al-Megrahi now faces a sentence imposed by a higher power."
Britain, meanwhile, walked a fine line - condemning al-Megrahi's reception without criticizing the decision to free him, which was made in Edinburgh under Scotland's separate judicial system.
The BBC reported that Britain was considering canceling a planned visit to Libya by Prince Andrew, who has visited the country several times in his role as a British trade ambassador. Andrew's office said a visit for next month was in the planning stages and that Buckingham Palace was taking advice from the Foreign Office.
The Foreign Office would not confirm that the visit would be canceled.
British officials also refuted claims the release was made to improve relations and bolster commercial ties - a view held by some victims' relatives in the U.S.
Miliband said any suggestion that the release was spurred by commercial interests was "a slur both on myself and on the government."
While Britain does have oil interests in Libya - notably a $900 million exploration deal between BP PLC and Libya's National Oil Co. - they are small compared to investments by Italy's Eni SpA.
Although the legal story of Lockerbie is now over, some argue that the full truth about the attack may never be known. Although Libya accepted formal responsibility for the bombing, many there see al-Megrahi as an innocent victim scapegoated by the West.
The Libyan's lawyers have argued the attack was the result of an Iranian-financed Palestinian plot, and a 2007 Scottish judicial review of al-Megrahi's case found grounds for an appeal of his conviction.
Some Lockerbie victims' relatives in Britain were disappointed when al-Megrahi dropped his appeal against his conviction, which he had to do in order to be freed. They had hoped new details about the bombing would come out at a future trial.
Even as he left prison, al-Megrahi protested his innocence.
"I say in the clearest possible terms, which I hope every person in every land will hear - all of this I have had to endure for something that I did not do," he said in a statement.
Scottish prosecutors formally dropped their appeal against the jail term imposed on the Lockerbie bomber. They had called the 27-year sentence too lenient and sought to have it extended.
Their appeal is now irrelevant. Al-Megrahi is free after serving just eight years.
Al-Megrahi's trial at a special Scottish court set up in The Netherlands, which came after years of diplomatic maneuvering, was a step toward normalizing relations between the West and Libya, which spent years under U.N. and U.S. sanctions because of the Lockerbie bombing.
Over the next few years, Gadhafi renounced terrorism, dismantled Libya's secret nuclear program, accepted his government's responsibility for the Lockerbie bombing and paid compensation to the victims' families.
Western energy companies - including Britain's BP - then moved into Libya in an effort to tap the country's vast oil and gas wealth.
Associated Press Writers Tarek el-Tablawy in Tripoli and Karolina Tagaris and Raphael G. Satter in London contributed to this report.