TRIPOLI, Libya >> Libya’s interim rulers declared the country liberated on Sunday after an eight-month civil war, launching the oil-rich nation on what is meant to be a two-year transition to democracy. But they laid out future plans with an Islamist tone that could rattle their Western backers.

The joyful ceremony formally marking the end of Moammar Gadhafi’s 42-year tyranny was also clouded by mounting pressure from the leaders of the NATO campaign that helped secure victory to investigate whether Gadhafi, dragged wounded but alive out of a drainage ditch last week, was then executed by his captors.

The circumstances of Gadhafi’s death remain unclear. However, critics said the gruesome spectacle of his blood-streaked body laid out as a trophy for a third day of public viewing in a commercial freezer tests the new leadership’s commitment to the rule of law.

Britain’s defense secretary, Philip Hammond, said the Libyan revolutionaries’ image had been "a little bit stained" by Gadhafi’s violent death. Both he and U.S. Secretary of State Hillary Rodham Clinton said a full investigation is necessary.

Gadhafi’s capture and the fall of his hometown of Sirte, the last loyalist stronghold, set the stage for the long-awaited declaration of liberation, delivered by the head of the National Transitional Council, Mustafa Abdul-Jalil.

He did not mention the circumstances surrounding Gadhafi’s death — mobile phone videos showed the wounded leader being taunted and beaten by a mob after his capture. But he urged his people to eschew hatred.

"You should only embrace honesty, patience, and mercy," Abdul-Jalil told a flag-waving crowd of several thousand at the declaration ceremony in the eastern city of Benghazi, the birthplace of the uprising against Gadhafi.

Abdul-Jalil laid out a vision for a new Libya with an Islamist tint, saying Islamic Sharia law would be the "basic source" of legislation and existing laws that contradict the teachings of Islam would be nullified.

He outlined several changes to align with Islamic law, including putting caps on interest for bank loans and lifting restrictions on the number of wives Libyan men can take. The Muslim holy book, the Quran, allows men up to four wives.

Abdul-Jalil thanked those who fought and fell in the war, saying they "are somewhere better than here, with God." Displaying his own piety, he then stepped aside from the podium and knelt to offer a prayer of thanks.

Using Sharia as the main source of legislation is stipulated in the constitution of neighboring Egypt. Still, Egyptian laws remain largely secular as Sharia does not cover all aspects of modern day life.

In Brussels, neither the EU nor NATO wanted to address the issue of Sharia law. A NATO official said it was for the Libyans to decide on the system in their own country.

"We trust the Libyan authorities to build an inclusive Libya, respectful of human rights and the rule of law," said an official who could not be identified for the same reason.

Libya’s revolt erupted in February as part of anti-government protests spreading across the Middle East. Islamist groups stand to gain ground in neighboring Tunisia and Egypt, which shook off their dictators several months ago. Tunisia has taken the biggest steps so far on the path to democracy, voting Sunday for a new assembly, while Egypt’s parliamentary election is set for next month.

Libya’s struggle has been the bloodiest so far in the region. Mass protests quickly turned into a civil war that killed thousands and paralyzed the country. Gadhafi loyalists held out for two more months after the fall of the capital of Tripoli in late August. Gadhafi’s hometown of Sirte fell last week, but Gadhafi’s son and one-time heir apparent, Seif al-Islam, apparently escaped with some of his supporters.

The anti-Gadhafi forces enjoyed strong Western political and military support during their revolt, especially from the U.S., Britain and France, and NATO airstrikes were key to their victory.

Abdul-Jalil paid tribute to the Gulf Cooperation Council, a six-nation alliance led by Saudi Arabia, the Arab League and the European Union. NATO performed its task with "efficiency and professionalism," he said.

President Barack Obama congratulated Libyans on the declaration.

"After four decades of brutal dictatorship and eight months of deadly conflict, the Libyan people can now celebrate their freedom and the beginning of a new era of promise," he said.

In Brussels, NATO Secretary-General Anders Fogh Rasmussen welcomed the declaration and said NATO’s mission in Libya "is very close to completion," referring to the alliance’s decision to end air patrols on Oct. 31.

In Libya, leaders have said a new interim government is to be formed within a month, following by elections for a constitutional assembly within eight months. Elections for a parliament and president would then follow in the year after that.

For a third day, Gadhafi’s body remained on display Sunday in a commercial freezer in the port city of Misrata, which suffered from a weeks-long bloody siege by regime forces in the spring. People have lined up since Friday to view the body, which was laid out on a mattress on the freezer floor. The bodies of Gadhafi’s son Muatassim and his ex-defense minister Abu Bakr Younis also were put on display, and people wearing surgical masks have filed past, snapping photos of the bodies.

It remains unclear what happened between the time Gadhafi was captured alive in Sirte on Thursday and arrived dead in Misrata later that day. Libyan leaders say he was killed in crossfire during battles for the city.

However, the New York-based group Human Rights Watch, which viewed the bodies, said video footage, photos and other information it obtained "indicate that they might have been executed after being detained."

"Finding out how they died matters," said Sarah Leah Whitson of Human Rights Watch. "It will set the tone for whether the new Libya will be ruled by law or by summary violence."

Mahmoud Jibril, the acting Libyan prime minister, said he would not oppose an inquiry into Gadhafi’s death, but there is "no reason" to doubt the credibility of an official report that he died in crossfire.

"Have you seen a video of somebody killing him? I haven’t seen any video tape or mobile film that shows somebody is killing Gadhafi," Jibril told reporters in Jordan where he was attending the World Economic Forum.

"What I told the press several times … (is) that the coroner says in the medical report that he (Gadhafi) was already wounded, taken out, put in that truck and on the way to the field hospital there was crossfire," Jibril said. He added that it was unclear whether the fatal bullet was fired by loyalists or revolutionary forces.

Addressing the celebrations around Gadhafi’s body, Jibril told the BBC in an interview on Sunday: "You have to appreciate the agony that people went through for 42 years."

Dr. Othman al-Zintani, Libya’s chief forensic pathologist, said he performed an autopsy that confirmed that Gadhafi was killed by a gunshot to the head. However, that finding did not shed light on the circumstances of his death, and al-Zintani said he could not elaborate until a full report has been sent to the attorney general.

Al-Zintani told The Associated Press Gadhafi’s body was removed from the freezer and taken to a secret location for the autopsy. He said he also examined the body of Muatassim.

The vast majority of Libyans seemed unconcerned about the circumstances of the hated leader’s death.

"If he (Gadhafi) was taken to court, this would create more chaos, and would encourage his supporters," said Salah Zlitni, 31, who owns a pizza parlor in downtown Tripoli. "Now it’s over."

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Associated Press writers Rami al-Shaheibi in Misrata, Libya and Slobodan Lekic in Brussels contributed to this report.