Iraq's President Jalal Talabani has accepted an invitation from his Iranian counterpart to discuss ways of tackling the violence in Iraq.
Mr Talabani's Tehran trip is to cover a range of issues, including security
Mr Talabani's office said he would meet President Mahmoud Ahmadinejad in Tehran on Saturday. Some reports say Syria's President Bashar al-Assad may attend.
The US has given a guarded response to the prospect of the talks in Tehran.
The Iraqi government has also said Syria and Iraq are planning to restore full diplomatic ties, cut in 1982.
The US has long accused Iran of providing bomb-making materials to Shia militia in Iraq and Syria of not doing enough to prevent insurgents crossing the border to smuggle arms and fighters.
Analysts say the US government has been more amenable to regional diplomacy since heavy losses for President George W Bush in 7 November mid-term elections.
However, Washington gave a cautious response to the news of Mr Talabani's trip to Tehran.
State department spokesman Tom Casey said Tehran had already indicated that it wanted to help reduce the violence in Iraq, but had not backed up the words with actions.
"The problem is not what they say," he told reporters. "The problem is what they do."
The BBC's David Loyn in Baghdad says as a Kurd President Talabani is a conciliatory figure in the Sunni/Shia divide and has been to Iran before.
Syria's foreign minister (l) pledged support to restore Iraqi security
Although he will talk about trade, industry and education, our correspondent says, this is not a normal visit and follows signals from the UK and the US about the constructive role Iran and Syria might play.
Shia legislators in Iraq said Syria's President Bashar al-Assad had been invited to the talks, but a spokesman for Mr Talabani dismissed the claims.
"This is a two-way bilateral summit, said Kameran Qaradaghi. "There was no invitation for a three-way summit."
The Iraqi president's trip to Tehran will follow one by his Prime Minister, Nouri Maliki, in September when he won a promise of support for his government in battling insurgents.
The announcement came as Syrian Foreign Minister Walid Muallim paid a key visit to Iraq - the highest-ranking Syrian official to travel to Iraq since the US-led invasion in 2003.
He promised his country's support in helping Iraq restore security.
Iraqi government spokesman Ali al-Dabbagh said: "The first step is restoring diplomatic relations before the delegation leaves, God willing."
Mr Maliki told Mr Muallim he was not prepared to let Iraq get caught up in Syria's differences with the US.
Syria has called for a timetable for the withdrawal of foreign troops
"[Syria] should settle these differences, but not at our cost," Mr Maliki said at a joint news conference with the Syrian foreign minister.
On Monday, a US military spokesman in Baghdad said between 70 and 100 foreign fighters were entering Iraq from Syria each month.
Mr Muallim said Syria wanted to be a partner with Iraq to increase security and political co-operation.
On Sunday, Mr Muallim called for the unity of Iraq to be preserved, and for a timetable for foreign troops to leave.
Escalating sectarian violence in recent months has increased pressure on the Iraqi government to stabilise the country.
In the past two days, two deputy health ministers have been attacked by gunmen. One of them was kidnapped.
Meanwhile, the US military says two members of its forces have been killed - one in Anbar province, in western Iraq, and one in a roadside bomb attack in Baghdad.