More than 100 people died on Thursday in widespread violence across Iraq, including a roadside bombing that killed four U.S. soldiers, as the number of Sunni mosques attacked rose to 168 following the bombing of a holy Shiite shrine and discussions on forming a unity government were suspended amid the strife.

Gunmen in Baqouba stopped three buses carrying factory workers, forced them out of the vehicles northeast of Baghdad and killed 47 of them, a provincial council member said.

The buses had been stopped at a checkpoint in the Nahrawan area, about 12 miles south of Baqouba, said Dhari Thuban, a member of the Diyala Provincial Council, before being burned and their passengers killed.

The motive for the killing was not immediately clear.

At least 47 other bodies were found scattered across Iraq, many of them shot execution-style and dumped in Shiite-dominated parts of Baghdad.

Three journalists working for Al-Arabiya television were found dead in Samarra, the site of Wednesday's Askariya mosque attack. Al-Arabiya is viewed in Iraq as favoring the United States.

In addition, four soldiers from the 101st Airborne Division were killed when their vehicle was hit by a roadside bomb north of Baghdad, the U.S. military said Thursday.

The soldiers assigned to the division's 1st Brigade Combat Team were killed on patrol Wednesday near Hawijah, 150 miles north of Baghdad, the military said in a statement.

The names of the victims were withheld pending notification of their families.

The hardline Sunni Clerical Association of Muslim Scholars said 168 Sunni mosques had been attacked, 10 imams killed and 15 abducted since the shrine attack. The Interior Ministry said it could only confirm figures for Baghdad, where 90 mosques were attacked in Baghdad, one cleric was killed, and one abducted.

Officials said at least 110 people had been killed across the country in violence believed triggered by the mosque attack.

The sectarian violence threatens to derail U.S. plans to form a new national unity government representing all factions, including Sunni Arabs, who form the backbone of the insurgency.

President Jalal Talabani, a Kurd, summoned political leaders to a meeting Thursday. But the biggest Sunni faction in the new parliament, the Iraqi Accordance Front, refused to attend, citing the attacks on Sunni mosques.

"We want a clear condemnation from the government which didn't do enough yesterday to curb those angry mobs," said Dr. Salman al-Jumaili, a member of the Front. "There was even a kind of cooperation with the government security forces in some places in attacking the Sunni mosques."

As the country veered ominously toward sectarian war, the government extended a curfew in Baghdad and Salaheddin province for two days. All leaves for Iraqi soldiers and police were canceled and personnel ordered to report to their units.

Sixteen people, eight of them civilians, died in a bombing Thursday in the center of Baqouba, 35 miles northeast of Baghdad.

The bombing, which targeted soldiers, was not seen as part of the sectarian fighting.

Radical Shiite cleric Muqtada al-Sadr accused the Iraqi government and U.S. forces of failing to protect the Samarra shrine, also known as the Golden Mosque, and ordered his militia to defend Shiite holy sites across Iraq.

"If the government had real sovereignty, then nothing like this would have happened," al-Sadr said a statement. "Brothers in the Mahdi Army must protect all Shiite shrines and mosques, especially in Samara."

The destruction of the gleaming dome of the 1,200-year-old Askariya shrine in Samarra sent crowds of angry Shiites into the streets. The crowds included members of al-Sadr's Mahdi Army and other Shiite militias that the United States wants abolished.

Sunni Clerical Association of Muslim Scholars spokesman Abdul-Salam al-Kubaisi blamed the violence on the country's top Shiite cleric, Grand Ayatollah Ali al-Sistani, and other Shiite religious leaders who called for demonstrations against the shrine attack.

"They are all fully aware that the Iraqi borders are open, and the streets are penetrated with those who want to create strife among Iraqis," al-Kubaisi said at a news briefing.

British Foreign Secretary Jack Straw said Thursday that he suspects Al Qaeda in Iraq, led by Abu Musab al-Zarqawi, was responsible for the devastating explosion at the Golden Mosque.

"There is not yet information about what caused this terrorist outrage, but al-Zarqawi and Al Qaeda have been linked as it has the hallmarks of their nihilism," Straw told a news conference in London. He called on leaders of Iraq's religious communities to defuse tensions caused by the attack.

Prime Minister Tony Blair said the attack was "an act of desperation as well as desecration."

Al-Kubaisi said U.S. Ambassador Zalmay Khalilzad enflamed the situation when he warned Monday that the United States would not continue to support institutions run by sectarian groups with links to armed militias.

"Without doubt, these statements mobilized all the Shiites," al-Kubaisi said. "It made them ready to go down to the street at any moment."

In Diyala, a religiously mixed province northeast of Baghdad, 47 bodies were found in a ditch. Officials said the victims appeared to have been stopped by gunmen, forced out of their cars and shot near Nahrawan, about 12 miles south of Baqouba. Most were aged between 20 and 50 and appeared to include both Sunnis and Shiites, police said.

Fighting broke out Thursday afternoon in Mahmoudiya, south of Baghdad, between militiamen from al-Sadr's Mahdi Army militia and Sunni gunmen. Two civilians were killed and five militiamen were injured, police Capt. Rashid al-Samaraie said.

Thousands of demonstrators carrying Shiite flags and banners marched Thursday through parts of Baghdad, Karbala, Kut, Tal Afar and the Shiite holy city of Najaf in protest against the shrine attack.

U.S. military units in the Baghdad area were told Thursday morning to halt all but essential travel. Commanders feared that convoys might be caught up in demonstrations or road blocks.

Also Thursday, gunmen fired automatic weapons and grenades at a Sunni mosque in Baqouba, killing one mosque employee and injuring two others, police said. Assailants also set fire to a Sunni mosque in eastern Baghdad, police said.

Eight Iraqi soldiers and eight civilians were killed when a soup vendor's cart packed with explosives detonated as a patrol passed in the center of Baqouba, police Maj. Falah al-Mohammedawi said. At least 20 people were injured in the blast.

The bullet-riddled bodies of a prominent Al-Arabyia TV female correspondent and two other Iraqi journalists, who had been covering Wednesday's explosion in Samarra, were found on the outskirts of the mostly Sunni Arab city 60 miles north of Baghdad.

The Associated Press contribute to this report.