Iraq's premier Monday called on ExxonMobil to respect the country's constitution in rare talks with the US firm's chief, an apparent reference to a deal with the Kurdish region Baghdad says is illegal.

Nuri al-Maliki also appeared to once again rule out production-sharing deals that Exxon has signed with Kurdistan, arguing that Iraq's substantial oil reserves "belong to all Iraqis," an oft-cited phrase in Iraq's constitution that central government officials see as justifying per-barrel service fees.

The meeting was the first between Maliki and Exxon chief Rex Tillerson since the firm signed an agreement in October 2011 for oil exploration with Kurdistan, angering the central government in Baghdad, which regards deals signed without the expressed approval of the federal oil ministry as illegal.

"Iraqis are partners in the oil that is discovered in any part of Iraq, they can not be partners in Basra and not partners in other areas", Maliki said, according to a statement from his office, referring to Iraq's southern oil-rich province.

The statement said Tillerson voiced keenness for Exxon to "continue its work and expand in Iraq" with the US firm's chief also apparently mentioning "important decisions in this area" that would be taken, though no further details were provided.

Exxon and Anglo-Dutch giant Shell completed a deal in January 2010 to develop production at West Qurna-1, an oil field in south Iraq, but late last year, the American company informed Baghdad that it wanted to sell its stake in the project, indicating it would focus on the controversial Kurdish deal.