Iranian President Mahmoud Ahmadinejad is deemed to demonstrate Iran's clout in Iraq during his landmark visit to the war-torn country on Sunday, challenging the United States which is seeking a long-term broad ties with Iraq.

Ahmadinejad will be the first Iranian president visiting Iraq since 1979 Islamic revolution in Iran.

The two countries fought a cruel eight-year war in 1980s. However, the relations have been picking up since the fall of Iraq's former president Saddam Hussein and his Sunni power in 2003.

Iran's clout in Iraq is getting stronger

Because of the natural bonds between the two Shiite-dominated countries, -- many Iraq's Shiite leaders lived in exile in Iran when Saddam was in power -- Iran's clout in Iraq is energizing in spheres of religion, economy and even politics.

A growing number of Iranian pilgrims travel to Shiite holy cities in Iraq, notably Najaf and Kalbara, during Shiite festivals.

The two countries, which have a trade volume of more than 2 billion U.S. dollars currently, are planning to enlarge economic cooperation.

Iraqi government spokesman Ali Dabbagh said last month that the top leaders of the two countries would talk about bilateral relations and joint projects during Ahmadinejad's upcoming visit to Iraq.

Prior to all of these, Iran's role in keeping Iraq's security and stability began to be cognized.

As Hassan al-Seneid, a Shiite lawmaker in Maliki's Dawa Party, put it to Xinhua, "The promotion of bilateral relations between Iraq and Iran, along with other neighboring countries will certainly enhance security and stability in Iraq and in whole region."

"This visit will shed light on the dark sides of relations between the two neighboring countries, which its background was shaped in the past by the bloody eight-year war. But there is other sides in our relations such as possibility of cooperation insecurity, economic, political and diplomatic fields," Seneid continued.

The Shiite lawmaker also expressed hope that Iran could hold a new round of talks with the U.S. so that they may solve their differences over security in Iraq.

The U.S. is aware of Iran's influence on Iraq very well. That's why it adopted a relative soft stance toward Iran over Iraqi issue compared with its tough standpoint on Iran's nuclear issue.

In seeking Iran's cooperation in helping quell the violence in Iraq, the U.S. has held three rounds of talks with its arch foe Iran over Iraqi security since last May.

Ahmadinejad's visit comes as challenge to US

Iran and the United States confronted each other tit-for-tat in many fields beyond Iraq.

Washington has been accusing Iran of developing nuclear weapons under the guise of civilian nuclear power project, which categorically rejected by Iran.