Prime Minister Nuri al-Maliki issued an open invitation for US firms to help rebuild Iraq on Tuesday, as his oil-rich nation closes the door on a nearly nine-year American military presence.

Hailing a new phase in the country's history, Maliki declared the long war-scarred nation was ready to build a new economy that held "limitless" opportunities for US firms.

"It is not now the generals but the businessmen and the corporations that are at the forefront" of Iraq's future, he told a business gathering just steps from the White House.

"Circumstances have improved because of better security," said Maliki, playing the role of salesman-in-chief for an economy that was ravaged by authoritarian rule and multilateral sanctions even before the war began in 2003.

"We are not satisfied with the number of US corporations in Iraq," he added. "All sectors of the economy are there, open for business for American business."

Oil is at the top of that list of sectors.

With massive proven reserves of 115 billion barrels of oil, the fourth largest in the world -- much of it untapped -- foreign oil companies are girding to return to the country.

Output today is around 2.5 million barrels per day, but could be nearly doubled by 2016 according to oil cartel OPEC.

But a political tug-of-war between the semi-autonomous Kurdish north and Baghdad has stalled efforts to create a new law governing the sector for the last three years.

While many companies, including ExxonMobil, have piled into Iraq despite the absence of a clear regulatory framework, there has often been confusion about their legal status.

Crafting such a law that makes the most of the country's resources, while attracting knowledgeable and deep-pocketed foreign firms, will be essential to putting the country on a sound footing.

Oil exports already account for around two thirds of Iraq gross domestic product, but actual revenues could be increased dramatically if production can be ramped up and if an estimated $100 billion of funds to rebuild the oil sector can be found.

Maliki gave little indication that a deal on the so-called hydrocarbons law was imminent, but said, "we do need a great package of new laws."

On Monday Maliki held talks with US President Barack Obama in an attempt to create a new paradigm in relations that have frequently been overshadowed by Iraq's descent into civil war and fierce divisions in the United States over the war's prosecution.