BAGHDAD, Iraq (CNN) -- Iraq's most powerful Sunni Muslim party quit talks to form a new government Thursday after reprisal attacks for the bombing of an important Shiite mosque.

Amid reports of more than 100 killings nationwide -- many of them Sunni Muslims -- the Sunni Accord Front announced it is leaving political unity talks after meeting with Iraqi President Jalal Talabani and Prime Minister Ibrahim al-Jaafari.

The Accord Front received 44 seats in December's election for the 275-member Iraqi parliament and has been working with Kurds, Shiites and other Sunnis to cobble together a government.

Including Sunnis in the government is seen as key to establishing law and order and defeating Iraq's insurgency, whose supporters are largely Sunni. Shiites were largely persecuted by ruling minority Sunnis during the reign of Iraqi leader Saddam Hussein.

The killings followed widespread Shiite protests after Wednesday's bombing of the Al-Askariya Shiite mosque -- also known as the Golden Mosque -- in Samarra.

Southeast of Baghdad, both Sunnis and Shiites joined to protest the bombing and reprisal attacks Thursday in the town of Kut, police said. Thousands of demonstrators marched through the streets saying that they are "all Iraqis."

Meanwhile, seven U.S. soldiers were killed in two roadside bombings north of Baghdad Wednesday, the U.S. military said.

Four soldiers from 1st Brigade Combat Team, 101st Airborne Division, were killed near Hawija.

Three Task Force Band of Brothers Soldiers from the 3rd Heavy Brigade Combat Team, 4th Infantry Division, were killed near Balad.

Their deaths brought the number of U.S. troops killed in the Iraq war to 2,285, according to military reports. 'Thumbprints of terrorists'

U.S. Maj. Gen. Rick Lynch told reporters in Baghdad Thursday that the mosque attack is under investigation, but said the military is "absolutely convinced the thumbprints of terrorists are all over this."

"It's clearly the signature of [Al Qaeda in Iraq leader Abu Musab al-Zarqawi] and terrorists and foreign fighters," Lynch said.

He praised the Iraqi government's "capable" leadership in reaction to the violence, such as enforcing curfews, calling for calm, recalling security forces on leave, and increasing security around shrines and political buildings.

He said coalition forces are deployed in reaction to the violence "but they are not in the lead." Bush: Bombing 'evil act'

President Bush, speaking at Thursday's White House Cabinet meeting, reiterated U.S. resolve to help Iraq rebuild the holy site.

"Voices of reason in all aspects of Iraqi life understand that this bombing is intended to create civil strife," Bush said, adding that the "act was an evil act. The destruction of a holy site is political act intending to create strife."

Iraqi President Talabani, speaking to reporters, urged all parties in Iraq to condemn the violence and agree on the need to have a government of national unity that can work toward keeping the peace and fighting terrorism.

"If the flames of division get enraged, God forbid, they won't help anyone," Talabani said. "No one will be spared. Putting those flames out is a sacred duty of all Iraqis and a must in order to achieve a unified democratic Iraq."

Sunnis killed

At least 54 Sunnis are believed to have been killed since the Golden Temple bombing including imams, worshippers and bystanders, according to police figures.

Separately, the bodies of 47 unidentified people who'd been shot were found Thursday southeast of Baquba.

While reporting on the Samarra attack, three journalists for Al-Arabiya television, including a female correspondent, were kidnapped and killed, police and the Arabic-language channel said.

An explosion killed 16 people Thursday and wounded 20 others in Baquba. Five people were killed and 10 others were wounded in another Baquba blast Thursday that's suspected of being a suicide bombing.

Iraqi police found six bodies Thursday -- all presumed to be Sunni -- in the Dora neighborhood of southern Baghdad.

Grand Ayatollah Ali al-Sistani, the most powerful Shiite cleric in Iraq, called on the government to take charge of the situation before the general public does.

"The Iraqi government is asked today to fulfill its responsibility to prevent attacks against holy shrines," he said Wednesday. "If its security forces are not able to secure these sites, then the believers are capable to do so with the help of Allah."

The nationwide violence ignited after the mosque was bombed by attackers dressed as Iraqi police commandos. The attack immediately enraged Iraq's majority Shiite Muslim community, sparking large protests in several cities.

Sunni boycott

Before announcing it was quitting talks to form a new government, the Iraqi Accord Front boycotted a meeting called by Iraqi President Talabani to discuss the Al-Askariya attack and sectarian tensions.

According to Iyad al-Samarrai, a senior member of the IAF, the group skipped the meeting because of reprisal attacks against Sunni mosques and what he said was the failure of the government condemn or prevent them.

Samarrai said at least 100 Sunni locations have been attacked since the bombing of the Shiite shrine, including Sunni political parties offices and mosques.

In a letter to the president's office, the Iraqi Accordance Front said it wants:

• Condemnation by the government and all parties of the attacks against Sunni mosques and locations.
• Investigation into the attacks.
• Compensation for all damages sustained.