US Secretary of State Condoleezza Rice has warned that the US will take action against countries destabilising Iraq.
Her statement comes hours after US forces stormed an Iranian consulate in the northern Iraqi town of Irbil - prompting condemnation from Tehran.
In a major policy speech, President George W Bush said the US would take a tough stance towards Iran and Syria, whom he accused of destabilising Iraq.
Mr Bush also vowed to increase troop numbers in Iraq by more than 20,000.
Democratic Senator Joseph Biden, the chairman of the influential Senate Foreign Relations Committee, said he thought Mr Bush's strategy was a "tragic mistake".
US troops raided the Iranian consulate in Irbil at about 0300 (0100 GMT), taking away computers and papers, according to Kurdish media and senior local officials.
Five US helicopters were used to drop troops on the roof of the consulate building, according to an Iranian website close to the revolutionary guards.
Vehicles cordoned off the access roads while troops broke down the front door, arrested five men inside and confiscated computers and documents, it said.
Iranian television has said they had been transferred to US central command in Baghdad.
Iran's foreign ministry condemned the attack, and summoned the ambassadors of Iraq and Switzerland which represents American interests in the Iranian capital to protest against it.
Ms Rice was speaking alongside new Defence Secretary Robert Gates and Chairman of the Joint Chiefs of Staff Peter Pace, to give details of the Bush administration's revamp of its Iraq policy.
The top US diplomat said Iran and Syria should "end their destabilising behaviour" in the region.
"The United States will defend its interests and those of our friends and allies in this vital region," she added.
She also said she was ready to meet Iran's leadership if it suspended its enrichment of uranium and pursuit of nuclear weapons.
"I repeat an offer that I have made several times, today. If Iran suspends its uranium enrichment, which is an international demand and not just an American one, then the United States is prepared to reverse 27 years of policy and I will met with my Iranian counterpart any time, anywhere."
On Wednesday, Mr Bush said fresh troops in Iraq would help to secure Baghdad's streets as part of the new strategy.
On Thursday, Mr Gates said he would seek to increase US forces by 92,000 soldiers and marines over the next five years for the long-term fight against terrorism.
In a poll conducted the day after Mr Bush's announcement, six in 10 Americans said they opposed an increase of troops in Iraq, with a substantial section of people saying they doubted that it would end the war more quickly.