U.S. President Barack Obama said Thursday he is examining the "full range" of military options, including a no-fly zone, if the revolt in Libya turns into a bloody stalemate and humanitarian disaster.

Accusing Moammar Gadhafi of encouraging violence against his citizens, Obama again called on the Libyan leader to stand down for the good of his country.

The Libyan opposition on Thursday flatly rejected a mediation proposal by Venezuelan President Hugo Chavez to find a peaceful solution to the crisis in the country, a spokesman said.

"We have a very clear statement. It's too late. Too much blood has been spilt," Mustafa Gheriani, a spokesman for the opposition's self-declared national council set up in the eastern city of Benghazi, told Agence France Presse.

The U.S. military is not opposed to imposing a no-fly zone over Libya, the Pentagon said on Thursday, despite a stream of skeptical comments by defense leaders.

The caution expressed by Defense Secretary Robert Gates and senior officers over a potential no-fly zone or other military action "should not be interpreted as somehow an opposition to doing this," Pentagon press secretary Geoff Morrell told MSNBC television.

Libya is on the verge of civil war, Russian President Dmitry Medvedev said on Thursday, in one of the starkest warnings yet by a world leader over the situation in the country.

"This is an extreme situation," he told Russia's Emergencies Minister Sergei Shoigu, according to state news agency ITAR-TASS.

U.S. Secretary of State Hillary Clinton said Wednesday that Iran is communicating with Hizbullah in a bid to shape events in the Arab world.

It was the first time that Clinton detailed alleged efforts by Tehran to meddle in the three-month wave of Arab revolts that has toppled presidents in Tunisia and Egypt, convulsed Libya and shaken Yemen, Bahrain and Oman.

Moammar Gadhafi and key aides will be probed over allegations they committed crimes against humanity while fending off the uprising in Libya, the International Criminal Court's prosecutor said Thursday.

"We have identified some individuals with de facto or formal authority, who have authority over the security forces," that have clamped down on a rebellion that started on February 15, Luis Moreno-Ocampo told journalists in The Hague.

The Arab League said Wednesday it would consider backing a no-fly zone over Libya to end its crackdown on anti-regime rebels, but ruled out supporting any direct foreign military intervention.

"The Arab countries cannot remain with their arms folded when the blood of the brotherly Libyan people is being shed," the league said in a resolution after a meeting of foreign ministers in Cairo.

Libyan rebels fought intense battles to repel Moammar Gadhafi's forces from the key eastern oil port of Brega Wednesday as the regime's biggest counter-offensive yet left at least 10 people dead.

Opposition fighters said they had finally pushed Gadhafi's men out of the town on the Mediterranean coast after a day of chaotic clashes, even as a government fighter jet fired two missiles near their victory celebrations.

Moammar Gadhafi warned the West on Wednesday against intervening to support the rebellion against him, saying that would unleash a "very bloody war" in which "thousands of Libyans would die."

Speaking live on state television, Gadhafi again blamed al-Qaida for the challenge to his 41-year iron-fisted rule, saying the objective was to control Libya's land and oil and promising to fight to the last man and woman.

At least 6,000 people have died since the start of the revolt against Libyan leader Moammar Gadhafi's regime two weeks ago, a spokesman for the Libyan Human Rights League said Wednesday.

"Victims in the whole country were 6,000," Ali Zeidan told reporters in Paris, adding that this included 3,000 in the capital Tripoli, 2,000 in the rebel-held second city Benghazi and 1,000 in other cities.