U.S. President Barack Obama Friday threatened defiant Libyan leader Moammar Gadhafi with military action unless he met specific, "non-negotiable" demands for a ceasefire, a halt to attacks on civilians and a retreat from rebel strongholds.

Obama said the world could not stand by because, if left unchecked, Gadhafi would commit atrocities in which thousands could die, adding that the Libyan strongman had been given "ample warning" to change his behavior.

Beleaguered Yemeni President Ali Abdullah Saleh ordered a state of emergency after regime loyalists on Friday killed at least 46 protesters, according to medics, in the bloodiest clash in weeks of unrest.

Witnesses said pro-Saleh "thugs" had rained bullets from rooftops around a square at Sanaa University, the center of demonstrations against Saleh, adding that more than 400 people were wounded.

Libya declared Friday an immediate ceasefire in the month-long battle against rebels fighting to overthrow strongman Moammar Gadhafi, but the insurgents dismissed it as a bluff and Washington demanded action, not words.

More than four hours after the announcement, rebels said they were still being attacked by Gadhafi loyalists, a claim Tripoli denied.

Saudi Arabia's king promised a multibillion dollar package of reforms, raises, cash, loans and apartments on Friday in what appeared to be the Arab world's most expensive attempt to appease residents inspired by the unrest that has swept two leaders from power.

He also announced 60,000 new jobs in the security forces — a move that would employ huge numbers of otherwise jobless young men, while bolstering his kingdom's ability to snuff out protests.

U.N. chief Ban Ki-moon is to join a summit on Libya between the European Union, the Arab League and the African Union in Paris on Saturday, the head of the League's secretariat said on Friday.

"The Arab League has received an invitation from France to take part in a one-day summit between the EU, the African Union and the Arab League tomorrow to discuss the situation in Libya and how to tackle it in the light of the latest U.N. resolution," Hisham Yussef said.

More than 30 anti-regime protesters were shot dead and over 100 wounded during a demonstration in the Yemeni capital Sanaa on Friday, medics and witnesses said.

According to witnesses, pro-regime "thugs" opened fire on protesters calling for the ouster of President Ali Abdullah Saleh from houses close to the square at Sanaa University.

Plainclothes Syrian security men broke up an apparently spontaneous demonstration by dozens of people after Friday prayers at the main mosque in Damascus, Agence France Presse reporters witnessed.

"God is greatest," a crowd inside the men's section of the Omayyad mosque started chanting in crescendo after prayers.

An indiscriminate attack on civilians in Benghazi would constitute "war crimes", the prosecutor of the International Criminal Court warned the Libyan government on Friday.

"Any indiscriminate attack against civilians would constitute war crimes," prosecutor Luis Moreno-Ocampo told journalists in The Hague.

Thousands of Bahraini Shiites defied martial law to renew their pro-democracy protests on Friday, as they gathered after prayers and to bury a victim of the security forces' bloody crackdown.

"We sacrifice blood and soul for Bahrain," they chanted, alongside calls for restraint and non-violence in the face of alleged crimes against international law committed by the Sunni-ruled kingdom's police and military.

Pro-democracy activists who spearheaded the mass rallies that ousted Egyptian strongman Hosni Mubarak were poised for a new protest Friday on the eve of a referendum on the military's transition plans.

The Coalition of the Youth of the Revolution called the rally in Cairo's Tahrir Square to urge voters to reject an amended constitution intended to underpin fresh presidential and parliamentary elections this year and a swift return to civilian rule.