MANAMA, Bahrain (AP) -- Security forces opened fire Friday on Bahraini protesters for a second straight day, wounding at least 50 people as thousands defied the government and marched toward Pearl Square in an uprising that sought to break the political grip of the Gulf nation's leaders.

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Once again, Bahrain authorities showed no hesitation in using force against demonstrators who ramped up demands to bring down the whole ruling monarchy.

U.S. President Barack Obama condemned the use of violence against the protesters in Bahrain, as well as in Libya and Yemen, where heavy crackdowns by old-guard regimes were reported. A Libyan doctor said 35 protesters were killed in the eastern city of Benghazi during a confrontation with security forces, while four people were killed and 48 were wounded during protests called as part of a "Friday of Rage" in Yemen.

The continuing wave of anger in the Arab world followed successful uprisings in Tunisia and Egypt, where hundreds of thousands of people celebrated the downfall of President Hosni Mubarak one week ago.

Critically injured protesters were again rushed to Manama's main Salmaniya hospital, which also received the dead and wounded after riot police smashed a protest encampment early Thursday in the landmark square.

Some doctors and medics on emergency medical teams were in tears as they tended to the wounded. X-rays showed bullets still lodged inside victims.

"This is a war," said Dr. Bassem Deif, an orthopedic surgeon examining people with bullet-shattered bones.

Of the 50 injured, seven were critically hurt, Health Ministry official said. Seven people have died in Bahrain's unrest this week, including five on Thursday, and more than 200 have been wounded.

Protesters on Friday described a chaotic scene of tear gas clouds, bullets coming from many directions and people slipping in pools of blood as they sought cover. Some claimed the gunfire came from either helicopters or sniper nests.

An Associated Press cameraman saw army units shooting anti-aircraft weapons, fitted on top of armored personnel carriers, above the protesters, in apparent warning shots and attempts to drive them back from security cordons about 200 yards (200 meters) from the square.

Then the soldiers turned firearms on the crowd, one marcher said.

"People started running in all directions and bullets were flying," said Ali al-Haji, a 27-year-old bank clerk. "I saw people getting shot in the legs, chest, and one man was bleeding from his head."

"My eyes were full of tear gas, there was shooting and there was a lot of panic," said Mohammed Abdullah, a 37-year-old businessman taking part in the protest.

The clash came hours after funeral mourners and worshippers at Friday prayers called for the toppling of the Western-allied monarchy in the tiny island nation that is home to the U.S. Navy's 5th Fleet, the centerpiece of the Pentagon's efforts to confront Iranian military influence. Some members of Bahrain's Sunni ruling system worry that Shiite powerhouse Iran could use Bahrain's majority Shiites as a further foothold in the region.

"I am deeply concerned about reports of violence in Bahrain, Libya and Yemen. The United States condemns the use of violence by governments against peaceful protesters in those countries and wherever else it may occur," Obama said. "The United States urges the governments of Bahrain, Libya and Yemen to show restraint in responding to peaceful protests and to respect the rights of their people."

Bahrain's king appointed Crown Prince Salman bin Hamad Al-Khalifa to lead a dialogue "with all parties," though it was unclear whether furious protesters would respond to the overture. Speaking on Bahrain state TV, Salman expressed condolences for "these painful days" and called for unity.

"We are at a crossroads," Salman said. "Youths are going out on the street believing that they have no future in the country, while others are going out to express their love and loyalty. But this country is for you all, for the Shiites and Sunnis."

The cries against the king and his inner circle - at a main Shiite mosque and at burials for those killed in Thursday's crushing attack - reflect a sharp escalation of the political uprising, which began with calls to weaken the Sunni monarchy's power and address claims of discrimination against the Shiite majority.

The mood, however, has turned toward defiance of the entire ruling system after the brutal crackdown in Pearl Square, which put the nation under emergency-style footing with military forces in key areas and checkpoints on main roads.

"The regime has broken something inside of me. ... All of these people gathered today have had something broken in them," said Ahmed Makki Abu Taki at the funeral for his 23-year-old brother, Mahmoud, who was killed in the pre-dawn sweep. "We used to demand for the prime minister to step down, but now our demand is for the ruling family to get out."

At a Shiite mosque in the village of Diraz, an anti-government hotbed, imam Isa Qassim called the Pearl Square assault a "massacre" and thousands of worshippers chanted: "The regime must go."

In a sign of Bahrain's deep divisions, government loyalists filled Manama's Grand Mosque to hear words of support for the monarchy and take part in a post-sermon march protected by security forces. Many arrived with Bahraini flags draped over the traditional white robes worn by Gulf men. Portraits of King Hamad bin Isa Al Khalifa were distributed.

"We must protect our country," said Adnan al-Qattan, the cleric leading prayers. "We are living in dangerous times."

He denounced attempts to "open the doors to evil and foreign influences" - an apparent reference to suspicions that Shiite powerhouse Iran could take advantages of any gains by Bahrain's Shiites, who account for about 70 percent of the population.

The pro-government gathering had many nonnative Bahrainis, including South Asians and Sunni Arabs from around the region. Shiite have long complained of policies giving Sunnis citizenship and jobs, including posts in security forces, to offset the Shiite majority.

Outside a Shiite village mosque, several thousand mourners buried three of the men killed in the crackdown.

Amid the Shiite rites, many chanted for the removal of the king and the entire Sunni dynasty that has ruled for more than two centuries in Bahrain - the first nation in the Gulf to feel the pressure for changes sweeping the Arab world.

"Our demands were peaceful and simple at first. We wanted the prime minister to step down,' Mohamed Ali, a 40-year-old civil servant, said as he choked back tears. "Now the demands are harsher and have reached the pinnacle of the pyramid. We want the whole government to fall."

At a funeral in the Shiite village of Karzkan, opposition leaders urged protesters to keep up their fight but not to seek revenge.

"We know they have weapons and they are trying to drag us into violence," said Sheik Ali Salman, the leader of the largest Shiite party, Al Wefaq, whose 18 lawmakers have resigned in protest from the 40-seat parliament.

The protesters had called for the monarchy to give up control over top government posts and all critical decisions and address deep grievances by Shiites, who claim they face systematic discrimination and poverty and are blocked from key roles in public service and the military.

Shiites have clashed with police before over their complaints, including in the 1990s. But the growing numbers of Sunnis joining the latest demonstrations surprised authorities, said Simon Henderson, a Gulf specialist at the Washington Institute for Near East Policy.

"The Sunnis seem to increasingly dislike what is a very paternalistic government," he said. "As far as the Gulf rulers are concerned, there's only one proper way with this and that is: be tough and be tough early."

In Libya, a doctor at al-Jalaa hospital in the eastern city of Benghazi said he saw the bodies of 35 people killed amid protests demanding the ouster of longtime leader Moammar Gadhafi. He said witnesses and survivors told him most of the victims came from an attempted protest outside a residential compound used by Gadhafi, with security forces firing on protesters demonstrating outside. The doctor spoke on condition his name not be used for fear of retaliation. More than a dozen protesters were shot to death in Libya on Thursday.

A ninth straight day of protests in Yemen saw anti-government demonstrators clash with police and supporters of longtime President Ali Abdullah Saleh - a key U.S. ally in fighting al-Qaida. Riot police fired tear gas and gunshots to disperse crowds in the capital of Sanaa and the port of Aden, where four people were killed. Someone threw what appeared to be a hand grenade into a crowd in the southern city of Taiz, wounding 48 people, witnesses said.

The U.N. High Commissioner for Human Rights, Navi Pillay, said the response of some governments in the Middle East and Africa to the demands of their people was "illegal and excessively heavy-handed," and she condemned the use of military-grade shotguns by Bahrain security forces. The European Union and Human Rights Watch urged Bahrain to order security forces to stop attacks on peaceful protesters.

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Brian Murphy in Dubai, United Arab Emirates, contributed to this report.