The discussions were confined to one session during a conference on Iraq stability, but they appeared to offer room for further interaction between the two nations -- which find themselves increasingly drawn toward common issues in Iraq as the nation's most influential allies.

The US ambassador to Iraq, Zalmay Khalilzad, said he exchanged views with Iranian delegates "directly and in the presence of others" at the gathering led by Iraq's neighbors and the five permanent members of the UN Security Council.

He declined to give details of the contacts -- calling them only "constructive and businesslike and problem-solving" -- but noted that he raised U.S. assertions that Shiite militias receive weapons and assistance across the border from Iran.

The chief Iranian envoy, Abbas Araghchi, said he restated his country's demands for a clear timetable for the withdrawal of US-led forces, which he insisted have made Iraq a magnet for extremists from across the Muslim world.

"Violence in Iraq is good for no country in the region," said Araghchi, deputy foreign minister for legal and international affairs, at a post-meeting news conference.

Araghchi said he did not meet privately with Khalilzad, but that all dialogue "was within the framework of the meeting" -- which he said had "very good interaction by all the delegations."

Khalilzad, too, called it a "first step."

"The discussions were limited and focused on Iraq and I don't want to speculate after that," he said.

For Iran, opening more direct contacts with Washington could help promote their shared interests in Iraq, including trying to stamp out Sunni-led insurgents. US officials, meanwhile, need the support of Iranian-allied political groups in Iraq to help contain Shiite militias.

The United States broke off ties with Iran after militants occupied the American Embassy in Tehran in the wake of the 1979 Islamic Revolution.

Iraq's foreign minister, Hoshyar Zebari, told reporters there were "direct exchanges and meetings and discussions" between the U.S. and Iranian delegation.

He also said the participants at the meeting agreed to take part in future groups to study ways to bolster Iraq's security, assist displaced people and improve fuel distribution and sales in one of OPEC's former heavyweights.

Zebari did not say whether Iran and the United States could join in these smaller "tactical committees."

But Araghchi, the Iranian envoy, insisted that the working groups should include only Iraq's neighbors and could consult with "countries who are players in the region" an apparent reference to the United States.

Iraq's prime minister, Nouri al-Maliki, opened the meeting with an appeal for international help to sever networks aiding extremists and warned that Iraq's growing sectarian bloodshed could spill across the Middle East.

Khalilzad also urged nations bordering Iraq which include Syria and Iran to expand assistance to al-Maliki's government, saying "the future of Iraq and the Middle East is the defining issue of our time."

"(Iraq) needs support in this battle that not only threatens Iraq but will spill over to all countries in the region," al-Maliki said shortly before mortar shells landed near the conference site and a car bomb exploded in a Shiite stronghold across the city.