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.