(Adds death toll from bombs)

By Paul Tait

BAGHDAD, July 25 (Reuters) - U.S. and Iraqi officials began work on Wednesday to team up with Iran to find an end to the bloodshed in Iraq whose security crisis was dramatised anew by two suicide bombs that killed 50 people.

Arch foes Iran and the United States agreed on Tuesday to set up a three-country security committee on Iraq's security crisis despite U.S. ambassador to Iraq, Ryan Crocker, accusing Tehran of stepping up support for militias there.

But Washington responded coolly to Tehran's overtures for higher-level talks.

The two suicide bombs exploded in Baghdad as Iraqis celebrated their soccer team's semi-final win over South Korea in the Asian Cup, killing 50 people and wounded 135.

One car bomb exploded near a crowd of jubilant Iraqis, killing 30 and wounding 75 in the Mansour area, police said. Another at an army checkpoint killed 20 people and wounded 60, many of them soccer fans celebrating nearby.

Sectarian violence and worsening chaos in Iraq has pushed the United States and Iran, which have not had diplomatic ties since shortly after Iran's 1979 revolution, to seek common ground, with Iraq asking both for help.

Two rounds of talks have had few concrete results apart from the agreement to establish a trilateral committee to investigate issues such as support for militias and al Qaeda in Iraq.

U.S. political and military representatives in Baghdad were working on how to set up the committee and areas which it would investigate after Tuesday's talks.

"They'll talk to the Iraqis, who will then talk to the Iranians and we'll see how we proceed from there," a U.S. embassy spokesman said.

Iraq's ambassador to the United States, Samir Sumaidaie, told reporters the security panel would focus on how to fight al Qaeda and Islamist militants as well as armed militias and how to better monitor and control Iraq's borders.

Washington accuses Shi'ite Muslim Iran of fomenting violence in Iraq. Iran denies the charge and blames the U.S.-led invasion to topple Saddam Hussein in 2003 for the bloodshed between Iraq's majority Shi'ite and minority Sunni Arabs.

Iranian Foreign Minister Manouchehr Mottaki was quoted on Wednesday as saying Iran was ready for higher-level talks with Washington if asked.

"It can be considered if Iran receives a formal request from America," Mottaki said.

But State Department spokesman Sean McCormack told reporters Washington had no plans to open higher-level talks. "We have an established channel with Ryan Crocker," he said, referring to the U.S. ambassador.

Iran's semi-official Fars news agency also quoted Mottaki as rejecting the accusations that Tehran backed Iraqi militants, saying the Americans were "trying to run away from their own mistakes".

PILGRIMS SHOT

Adding to tension, unidentified gunmen set up a fake checkpoint in a southern area of Baghdad on Wednesday and fired on Iranian pilgrims returning from the holy Shi'ite city of Kerbala, seriously wounding seven of them, police said.

Tuesday's talks came less than two months before Crocker and U.S. military commander General David Petraeus are due to present a crucial report to the U.S. Congress on Iraq's political and security progress.

Iraqi Prime Minister Nuri al-Maliki's fractured government is under growing pressure from Washington to meet a series of political benchmarks aimed at promoting national reconciliation before Congress receives the progress report in mid-September.

Underscoring the difficulties Maliki faces, the Accordance Front, parliament's main Sunni bloc, said on Wednesday its ministers would suspend work for a week to push the government to give them a greater say in security matters.

The Front suspended participation in cabinet meetings last month. (With additional reporting by Stuart Grudgings in Washington, Mariam Karouny in Baghdad and Parisa Hafezi in Tehran)

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