BAGHDAD — Iraq’s most influential Shiite politician said yesterday that America had not backed up claims that Iran is fueling violence here, underscoring a wide gap on the issue between Washington and the Shiite-led Baghdad government.

A draft bill to ease curbs on ex-Saddam Hussein loyalists in government services also drew sharp criticism from Shiite lawmakers, opening old wounds at a time when America is pressing the Iraqis for compromise for the sake of national unity.

The Americans have long accused the Iranians of arming and training Shiite militias, including some linked to the American-backed government of Prime Minister al-Maliki, who is a Shiite.

American officials have also alleged that Iran has provided weapons used to kill Americans — a charge the Iranians deny.

“These are only accusations raised by the multinational forces and I think these accusations need more proof,” the leader of the Supreme Islamic Iraq Council, Abdul-Aziz al-Hakim, told reporters. Mr. Hakim, who has been undergoing treatment for lung cancer in Iran, said the Iranians have insisted in meetings with Iraqi officials that “their true will is to support the Iraqi government” and to promote stability. “They have a long history of standing by the Iraqi people and that is their official stance that is presented to the press without any hesitation,” he said.

Mr. Hakim spent years in exile in Iran during Saddam’s regime and is considered closer to the Iranians than any of the major Iraqi Shiite leaders. His party has also closely cooperated with American authorities since the 2003 collapse of Saddam’s regime, and he has met with President Bush in the Oval Office.

His comments were made ahead of a new round of talks between American and Iranian officials here over ways to promote stability in Iraq and exploit the sharp downturn in violence since America sent 30,000 reinforcements early this year. No date for the next American-Iranian talks has been announced. The Americans are expected to raise concerns about Iranian influence among Shiite armed groups, although American officials have said they believe the flow of Iranian arms has been curtailed.

This month, the American military released nine Iranians who had been held in Iraq for months. They included two accused of being members of the elite Quds Force suspected of arming Shiite extremists.

But the American military has blamed an Iranian-backed Shiite cell for a bombing Friday in a Baghdad market that killed 15 people — the deadliest attack in the heart of the capital in more than two months. An American military spokesman, Rear Admiral Gregory Smith, stressed he was not accusing Iran of ordering the attack. Nonetheless, Iran dismissed any suggestion that it was at fault.

“Contradictory reports have been heard about the bombing. But remarks by the Americans were made with the aim of making propaganda against Iran,” a spokesman for Iran’s Foreign Ministry, Mohammad Ali Hosseini, told reporters yesterday in Tehran. Although major Kurdish and Shiite parties maintain ties to Iran, suspicion of the Iranians runs deep within the country’s Sunni Arab community, including those groups that have abandoned the insurgency and agreed to work with American forces.

Sunni fears of Iranian domination are among the obstacles standing in the way of reconciliation among Iraq’s religious and ethnic communities.

Another hurdle has been Sunni complaints that they have been marginalized politically by regulations that banned former members of Saddam’s Baath Party from holding government jobs or running for public office.

America has been pressing the Iraqis to relax the ban to allow thousands of lower-ranking Baathists to regain their posts.