Mr Mottaki is attending meetings in Davos
Real change in Washington's policy in the Middle East would enable Iran to have a "co-operative" attitude towards the US, Iran's foreign minister says.
Manouchehr Mottaki was speaking at a session at the World Economic Forum.
A day earlier, Iran's president, responding to an overture by the new US president, said the US should apologise for its past "crimes" against Iran.
This was the first official response to Barack Obama's offer to extend a hand if Iran "unclenched its fist".
Mr Obama has emphasised the need to engage with Iran, a country his predecessor viewed as among the most dangerous in the Middle East.
"We do believe that if the new administration of the United States, as Mr Obama said, is going to change its policies, not in saying but in practice, definitely they will find the region in a co-operative approach and reaction," Mr Mottaki told a panel in Davos.
"And Iran is not excluded from this general understanding in our region."
Iran had noted Mr Obama's stated intention to pull troops out of Iraq and believed he should withdraw from Afghanistan, too, Mr Mottaki said.
Quoted by Reuters news agency, he praised Mr Obama for having "courage" to move away from the policies of George W Bush and an era of "might equals right".
"We are in a turning point. We are at a milestone now," Mr Mottaki said.
In his televised address on Wednesday, President Mahmoud Ahmadinejad said the US had "stood against the Iranian people in the past 60 years".
Mr Ahmadinejad's remarks were the first since Mr Obama took office
"Those who speak of change must apologise to the Iranian people and try to repair their past crimes," he said in the western Iranian region of Kermanshah.
Iranian anger remains over issues such as Washington's support for the Iranian coup of 1953, for Saddam Hussein in the Iran-Iraq war of the 1980s, and for Israel, and also over its wars in Afghanistan and Iraq.
The BBC's Jon Leyne in Tehran describes the speech as one of Mr Ahmadinejad's strongest tirades against the US.
Relations between Washington and Tehran reached new lows in recent years over attempts by the US and its allies in the UN to curtail Iran's nuclear programme over fears it is trying to build nuclear weapons.
Tehran says its programme is to develop civilian nuclear power only.
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