Iran remains the "real problem" for Iraq, the US nominee for ambassador to Baghdad has said, pledging to work to ensure Tehran respects Iraqi sovereignty.

"The real problem in the region for Iraq is its ancient neighbour, Iran," Christopher Hill told the Senate Foreign Relations Committee at a confirmation hearing on Wednesday.

"We believe and the Iraqis definitely believe that Iran needs to respect Iraqi sovereignty and respect their internal affairs," the veteran diplomat said.

The US and Iraqi governments have accused Iran in the past of interfering in Iraqi politics and of backing armed groups.

However, if an ongoing review of US-Iran relations concludes that he should pursue high-level contacts with Iranian diplomats, Hill said, then "I would be most pleased to do that".

Last week, Barack Obama, the US president, issued a videotaped message to Iran, offering a "new beginning" in US-Iranian relations.

Hill is a career foreign service diplomat who served as the lead US negotiator in six-party talks over North Korea's nuclear programme during the administration of George Bush, Obama's predecessor.

'Crucial phase'

He also said that the planned withdrawal of US forces from Iraq posed challenges for maintaining security and said he would make strengthening Iraq's security services and government his priority.

"I think we are in a really crucial phase," he said.

"The task of drawing down forces tends to be more difficult than flowing in forces."

The committee was expected to send the nomination to the full senate, where there has been Republican opposition to his appointment.

Republican senators have accused Hill of going back on pledges to keep North Korea's human rights record central to six-party talks on dismantling its nuclear programme, a charge he denies.

Hill told the senate committee that if he is confirmed, he would be ready to head to Baghdad the next day.