Iraq's President Jalal Talabani has said he is confident of Iran's support in fighting terrorism and helping secure a stable future for his country.
Jalal Talabani is the first Iraqi head of state to visit Iran since the 1960s
Mr Talabani was speaking during the first visit by an Iraqi head of state to Tehran in almost four decades.
The trip is a sign of closer relations between the Shia-dominated Iraqi government and mainly Shia Iran.
However, Iraqi and US officials accuse Iran of doing too little to stop insurgents crossing into Iraq.
Speaking after talks with Mr Talabani, Iran's President Mahmoud Ahmadinejad repeated Tehran's staunch denial of the allegation.
He also promised his country's total support for Iraq's independence.
"A popular, independent and developed Iraq will be the best friend of the Iranian nation," Mr Ahmadinejad said.
"We totally support the political process that the Iraqi nation is undergoing that will... guarantee its territorial integrity, independence and progress."
Mr Talabani, who is expected to meet Iran's foreign minister and top security official during his three-day visit, is accompanied by Iraq's national security adviser, Muwafaq al-Rubaie.
"We are sure that we will enjoy the Iranian government's co-operation in our struggle against terrorism," said Mr Talabani, who leads the Kurdish element in Iraq's government.
The BBC's Frances Harrison in Tehran says diplomatic niceties aside, it is likely Iraqi officials will be pushing Iran for more support in countering the insurgency, especially after allegations from Britain that Iran has a hand in destabilising southern Iraq.
Questions have been raised over the influence of Iranian Shia clerics in Iraq, where tensions between the Shia majority and Sunni minority are rising.
Speaking at a national reconciliation conference in Cairo on Sunday, Mr Talabani said he was "willing to speak to insurgents if they want to talk to him".
However, he warned that supporters of Saddam Hussein and religious extremists had no role in the country's political process.
Mr Talabani's trip to Iran is the first by an Iraqi head of state since former President Abdul Rahman Muhammad Arif visited in the late 1960s. The two countries were at war from 1980 to 1988.