President Mahmoud Ahmadinejad arrived in Baghdad on Sunday, the first Iranian president to visit Iraq since the two neighbours fought a protracted war in the 1980s that killed a million people.
Iraqi officials said he arrived after making the short flight from neighbouring Iran. Ahmadinejad is expected to go straight into talks with Iraqi President Jalal Talabani and Prime Minister Nuri al-Maliki.
His trip is expected to be as much about symbolism as it will be about cementing ties between Shi'ite Iran and Baghdad's Shi'ite-led government. It will be closely watched by arch-foe the United States, which has more than 150,000 troops in Iraq.
Ahmadinejad, known for his provocative rhetoric, has said that the United States is to blame for violence in Iraq and called for US troops to leave.
"Security for Iraq is security for Iran, and this does not suit the enemy because they do not want stability for the region, so they can continue their meddling in its affairs and justify the presence of its military," he said in an interview with Iraqi journalists published in local newspapers.
Speaking on the eve of his trip to Baghdad, Ahmadinejad said his visit would help improve security in Iraq.
"It will surely help strengthen the Iraqi nation and the government ... and peace and security in the region," he told Iranian state television. "Withdrawal of the occupying forces is in everyone's advantage," he added.
Washington says Tehran supplies weapons and training to Shi'ite Muslim militias to attack U.S. troops, a charge Tehran denies. The two countries are also at odds over Iran's nuclear programme.
Iran's influence in Iraq has grown substantially since the 2003 U.S.-led invasion ousted Saddam Hussein, and analysts say Ahmadinejad will use his visit to show Washington that Tehran is a power in Iraq that cannot be ignored or sidelined.
Iranian deputy Foreign Minister Alireza Sheikh-Attar said Ahmadinejad would sign five to 10 agreements during his trip.
No US role
US officials in Baghdad say they will play no role in Ahmadinejad's visit and that the U.S. military will not be involved in protecting him as he travels around.
When Ahmadinejad, the first Iranian president to visit since the 1979 Islamic Revolution, flew into Baghdad international airport, his plane was controlled by Iraqi air controllers.
But from his plane, Ahmadinejad would probably have seen the rows of American armoured vehicles and helicopters at a giant US military base next to the airport.
And unlike the strict secrecy that surrounds visits by U.S. President George W. Bush to reduce the risk of an insurgent attack, Ahmadinejad's trip has been well-flagged. Also, unlike Bush, he will be spending the night.
Details of the schedule for the first day of his visit made public so far suggest he may not enter the U.S.-protected Green Zone that houses Iraqi ministries and the U.S. embassy.
Instead Ahmadinejad will hold talks at Talabani's house in the central Karrada district and stay the night there, Iraqi officials said.
Besides meeting Maliki and Talabani, he will also meet Vice President Adel Abdul-Mahdi.
Abdul-Mahdi told Reuters on Saturday that Iraq wanted to use Ahmadinejad's visit to resolve a number of long-running disputes including defining their common border, a flashpoint issue that sparked the 1980-88 war between the two countries.
Analysts say that despite its reported support for Shi'ite militias, Iran prefers a stable if not necessarily strong Iraq. It was widely seen to be behind a ceasefire called by Shi'ite cleric and Mehdi Army leader Moqtada al-Sadr last August.
Iraq's Shi'ite leaders have close ties with Iran as many lived in exile there during Saddam's rule, although its influence over them is unclear.
(Additional reporting by Mariam Karouny, Wisam Mohammad and Mohammed Abbas)