President Barack Obama hailed Muammar Gaddafi's death on Thursday as a warning to authoritarian leaders across the Middle East that iron-fisted rule 'inevitably comes to an end,' and as vindication for his cautious strategy toward Libya.

Obama joined US politicians and ordinary Americans in welcoming the demise of Gaddafi, who was for decades regarded as a nemesis of American presidents, and also claimed some of the credit for the Libyan strongman's downfall.

But he also appeared to distance Washington from deeper entanglement in the North African oil-producing nation at a time of economic woes at home, placing responsibility for Libya's future squarely on the shoulders of the fractious interim leadership in Tripoli.

'This marks the end of a long and painful chapter for the people of Libya who now have the opportunity to determine their own destiny in a new and democratic Libya,' Obama said in the White House Rose Garden.

Obama made clear he considered Gaddafi's death a validation of his 'leading from behind' strategy that had drawn criticism at home for casting the United States in a support role in the Nato air assault in Libya. Some of his Republican foes see it as an 'Obama doctrine' that abdicates US global leadership.

He also issued a veiled warning to Syrian President Bashar al-Assad and other long-entrenched Middle Eastern leaders resisting home-grown democracy movements to take heed of Gaddafi's fate.

'Our leadership at Nato has helped guide our coalition. Without putting a single US service member on the ground, we achieved our objectives, and our Nato mission will soon come to an end,' Obama said in a televised statement to a US public already weary of long wars in Iraq and Afghanistan.

A Nato official said an unmanned US aircraft took part in strikes on Thursday in Libya, but it was unclear whether US or French airpower struck Gaddafi's convoy believed to have been carrying him near his hometown of Sirte.

The United States had led the initial air strikes on Gaddafi's forces but quickly handed the lead over to Nato, while taking a back seat to Britain and France.

Gaddafi's death is unlikely to give Obama any lasting help in a 2012 presidential election expected to be decided by the state of the stumbling economy and stagnant job market. The raid he ordered in May that killed al Qaeda leader Osama bin Laden gave him only a short-lived boost in the polls.

The US reaction to Gaddafi's death reflected a tortured history with an Arab leader long viewed by Americans as a villain for his government's links to the 1988 bombing of a Pan Am flight over Lockerbie, Scotland, and a 1986 disco bombing in Berlin that targeted US servicemen.

Obama also touted Gaddafi's death as a stark message to other authoritarian rulers in the Middle East where revolts upended longtime leaders in Egypt and Tunisia this year.

Washington has demanded that Assad halt his crackdown on democracy protests in Syria and step down, and is pressing Yemen's longtime president, Ali Abdullah Saleh, to leave office in the face of political upheaval.

Obama has also condemned Iran's human rights record and is seeking further sanctions against Tehran over an alleged foiled plot to assassinate the Saudi ambassador in Washington.

'For the region, today's events prove once more that the rule of an iron fist inevitably comes to an end,' Obama said.

Obama said the United States would be a partner to Libya's interim government and urged a swift transition to democracy but made no specific promises of aid.

Justice for Lockerbie victims

Relatives of American victims of the flight blown up over Lockerbie by Libyan agents 23 years ago said justice was served with Gaddafi's death as he fled his hometown and final bastion.

'I hope he's in hell with Hitler,' said Kathy Tedeschi, whose first husband, Bill Daniels, was among the 270 people killed in the bombing of Pan Am Flight 103.

Politicians across the spectrum also welcomed Gaddafi's death, which could help Obama undercut Republican efforts to question his national security credentials in his 2012 re-election bid.

Republican presidential front-runner Mitt Romney, who once called Obama's Libya strategy 'muddled,' said, 'The world is a better place with Gaddafi gone.'

'The death of Muammar Gaddafi marks an end to the first phase of the Libyan revolution,' said Senator John McCain, the top Republican on the Armed Services Committee and 2008 Republican presidential candidate.

Senator Carl Levin, a senior Democrat, said, 'The success of the Libyan people in rising up to overthrow a tyrant is a blow against dictatorship everywhere.'

Obama had faced criticism for an initially slow response to the Libyan uprising and then set strict limits on the US role in the Nato air assault, which was sanctioned by the United Nations as a means of stopping the massacre of civilians.

But the White House felt its approach bore fruit when rebel forces took Tripoli, and it used Gaddafi's death to reinforce that argument.

Republicans were not expected to ease their accusations that Obama undermined U.S. global prestige with a 'leading from behind' approach to 'Arab Spring' popular revolts that have engulfed friends and foes alike.-Reuters