Iran has been accused of meddling in its neighbours' politics and trying to "wreak havoc" across the Middle East by the leader of the party which won most seats in Iraq's election.
Ayad Allawi, whose nationalist Iraqiya block won Iraq's election in March but looks like being frozen out of power by an Iranian-backed alliance, was speaking after a visit by Iran's president, Mahmoud Ahmadinejad, to Lebanon last week.
Mr Ahmadinejad asserted its backing for Hezbollah, the Shia Lebanese militia dedicated to fighting Israel. But Iran has also been accused of funding terror groups across the region, including Iraq.
"We know that unfortunately Iran is trying to wreak havoc on the region, and trying to destabilise the region by destabilising Iraq, and destabilising Lebanon and destabilising the Palestinian issue," Mr Allawi said in an interview with CNN.
"And this is where unfortunately Iraq and the rest of the greater Mideast is falling victim to these terrorists, who are definitely Iran-financed and supported by various governments in the region."
Mr Allawi is currently fighting for his political life. After winning 91 seats out of 325 in the election, two more than the State of Law coalition of the prime minister, Nouri al-Maliki, he insisted on the right to try to form a government.
However, State of Law, a largely secular Shia grouping, turned instead to other Shia parties. Last month, it announced an alliance with the Sadrist block, the violently anti-American religious party led by a radical cleric, Moqtada al-Sadr.
The Sadrists have always boasted that they are not controlled by any "outside force", but Mr Sadr is now living and studying in Iran and Iranian officials played a strong role in organising the alliance.
Mr Maliki now needs only to do a deal with the parties of the semi-autonomous Kurdistan Autonomous Region, who were allies before the election, to return to power.
Mr Allawi's harshly-worded criticism of Iran may be targeted at the Kurds.
They have previously said they would only join a government if it was cross-sectarian, including representatives of the Sunni minority, most of whom supported Iraqiya.
Iran is also in the middle of a crackdown on Kurdish separatist forces inside its own borders.
But Mr Allawi, though himself a Shia, is also close to Saudi Arabia and other Sunni-led Middle Eastern states with a strong fear of rising Iran.
Mr Ahmadinejad's diplomatic push in recent months, strengthening ties with Syria and Turkey and asserting the role of Hezbollah and Hamas, the radical Palestinian faction, has marginalised local allies of Sunni states.
Visits on Sunday and Monday by President Bashar al-Asad of Syria to Saudi Arabia and Mr Maliki himself to meet senior officials in Iran may be aimed at outlining final terms for a Maliki-led government.
Saudi Arabia and Syria both distrust Mr Maliki but may have to come to terms with his determination to hang on to office.
The Iranian ambassador to Iraq dismissed Mr Allawi's comments.
"These comments are not true," Hassan Danaeifar said. "He makes such remarks on the threshold of trips to other nations, and they are baseless.
"These comments are old and these friends have made them so many times that nobody listens."