Iraq is teetering on the brink of civil war, United Nations Secretary General Kofi Annan has said publicly.
Mr Annan's verdict came after one of Iraq's bloodiest weeks
Mr Annan said concerted action to dampen the vicious sectarian violence gripping Iraq was urgently needed.
The continuing and escalating violence in Iraq has prompted a flurry of diplomatic activity this week.
Iraqi President Jalal Talabani is due to meet Iran's supreme leader, while US President George W Bush goes to Jordan a day later to meet the Iraqi PM.
Speaking at the UN, Mr Annan said the increasingly brutal attacks by Shias and Sunnis in Iraq were dragging the country towards a dangerous level of violence.
"I think given the developments on the ground, unless something is done drastically and urgently to arrest the deteriorating situation, we could be there. In fact we almost are there," he told reporters.
Mr Ahmadinejad (right) said Iran would offer what help it could
But Mr Annan's analysis was not fully backed up by the US.
Speaking en route to the Baltic for the Nato summit, national security adviser Stephen Hadley admitted that the conflict in Iraq was entering "a new phase".
But he added: "The Iraqis don't talk of it as civil war."
"We're clearly in a new phase characterised by this increasing sectarian violence that requires us obviously to adapt to that new phase," he said.
Mr Hadley said he expected Iraqi Prime Minister Nouri al-Maliki to raise the issue of possible talks with Iran and Syria when he meets Mr Bush in Jordan.
Given a red-carpet welcome in Iran, Mr Talabani called on Iran to provide "comprehensive help" to improve his country's security situation.
Iranian television quoted the Iraqi president as saying: "We are in dire need of Iran's help in establishing security and stability in Iraq."
Deadly attacks killed more than 200 in Baghdad last Thursday
Iranian President Mahmoud Ahmadinejad told him Iran would do what it could.
The US and UK have repeatedly accused Iran of impeding efforts to stabilise Iraq.
But Mr Ahmadinejad said a secure, progressive and powerful Iraq was in the interests of Iran and the whole region.
He said the situation inflicted on Iraq by its enemies pained all Iranians and Muslims.
Iranian officials said Iran had been trying to organise a summit including Mr Ahmadinejad, Mr Talabani and Syrian President Bashar al-Assad but that Damascus had not responded to the invitation.
The BBC's Frances Harrison in Tehran says some have suggested Iran wants to keep the US bogged down in Iraq to prevent it attacking Iran in the future over its nuclear programme.
But she says it seems Iran is increasingly concerned about the uncontrollable level of violence in Iraq.
Last week's multiple car bomb attacks in Baghdad's Sadr City - in which more than 200 people were killed - were the deadliest in Iraq since the US-led invasion of 2003.
Last week, the UN said violent deaths among civilians hit a record high in October, with more than 3,700 people losing their lives - the majority in sectarian attacks.