"[US commander in Iraq General Ray] Odierno and I are confident that Iraqi troops are up to the challenges of securing these urban areas and soon their entire nation, but we stand ready to assist if called upon," Gates said.

US departure unclear

"Nobody's the boss or the occupier or however you want to put it, but there's a real sense of empowerment by the Iraqis," he said.

Gates avoided commenting on whether American forces may stay beyond their departure deadline by the end of 2011.

Al-Maliki suggested last week that if Iraq needs more security help, it might ask for an extension of the US military's commitment.

"What happens beyond 2011 is a subject best left to the end of 2010 or 2011 itself," Gates said.

In a joint press conference with Abdel Qader Obeidi, Iraq's defence minister, Gates urged the country's Shia, Sunni and Kurdish communities to settle their power-sharing disputes while American troops remain on the ground.

"We will continue to support Iraq's progress toward national unity," he said.

Oil disputes

"We are also willing to assist in resolving disputes over boundaries and hydrocarbons, disputes that require continued commitment to the political process by word and deed," he said.

Kurds want to incorporate oil-rich areas in the north into their semi-autonomous region, while other groups want it to remain under central government control.

Gates was due to visit the Kurdish region on Wednesday and meet Masoud Barzani, the Kurdish president.

Barzani has signed oil deals with foreign firms that Hussein al-Shahristani, the Iraqi oil minister, deems illegal.

"The Arab-Kurd dimension is probably the most pressing one at the moment in terms of the issues that really need to get dealt with to consolidate our security gains," a senior US official said on condition of anonymity.