The officials are expected to discuss Baghdad's interest in acquiring US fighter jets to counter possible threats from neighbouring nations after US forces leave the country.

Last week, al-Maliki travelled to the US to meet Barack Obama, the US president, and Joe Biden, the US vice president, and Hillary Clinton, the US secretary of state.

Regional harmony

Gates is also expected to visit Iraq's restive Kurdish region, where challengers made a surprisingly strong showing in regional elections over the weekend.

Kurds were united in their hard line in disputes with Iraq's Arabs over oil-rich territory, which threaten to erupt into new violence even as the US military prepares to withdraw its forces by the end of 2011.

Gates will hold talks with Masoud Barzani, president of the Kurdistan region, which has signed oil deals with foreign firms that Hussein al-Shahristani, the Iraqi oil minister, deems illegal.

Last week, Obama pressed al-Maliki to make room in his government and security forces for all ethnic and religious groups.

US officials, while praising improvement in Iraqi security forces, remain deeply concerned that al-Maliki's Shia-dominated government has been unable or unwilling to reconcile with the country's minority Sunni Muslims and Kurds.

The US defence secretary is likely to reinforce the talks held last week between al-Maliki and Obama, in which both countries said they aimed to establish "more normal" bilateral ties.