US Defence Secretary Leon Panetta has warned Iran that it should not meddle in Iraq when American forces leave the country at the end of this year.

The Pentagon chief said that even after the last of the 39,000 combat troops are out of Iraq, the US will maintain a significant presence in the Middle East.

"As the president announced, we are going to wind down our combat forces in Iraq by the end of this year," he told US service personnel during a visit to Tokyo.

"The mission there was to develop an Iraq that could govern and secure itself and we will maintain a long-term relationship with Iraq."

"The message to Iran and everybody else that might have any ideas there is that the US is going to have a presence in the region for a long time to come."

Mr Panetta's comments come at the end of a three-day visit to Japan, part of a tour of Asian allies where he has emphasised Washington's commitment to the Pacific theatre, despite deep cuts to the US military budget.

They also come days after US Secretary of State Hillary Clinton aired similar views after Iranian President Mahmoud Ahmadinejad said Tehran had "special relations" with Baghdad.

"No one, most particularly Iran, should miscalculate about our continuing commitment to and with the Iraqis going forward," Clinton said in an interview with CNN.