Analysts said Mr Rouhani's inauguration speech was conciliatory in tone
The US has offered Iran a "willing partnership", after President Hassan Rouhani was inaugurated in Tehran.
The White House said Iran now had a chance to allay fears over its nuclear programme and meet its international obligations.
Mr Rouhani used his inauguration speech to promise a government of moderation for all Iranians, but also called for international sanctions to be lifted.
US-Iran relations soured under ex-President Mahmoud Ahmadinejad.
He regularly made inflammatory speeches denouncing the US and Israel.
Analysts said Mr Rouhani's inauguration speech was conciliatory in tone, and he appeared to be reaching out to groups inside and outside Iran.
"In international interactions, my government will try to build mutual trust between Iran and the regional and global countries," he told parliament.
"Transparency is the key to open a new chapter in mutual trust. And the transparency we are talking about cannot be a one-way transparency, and without practical measures in our bilateral and multilateral relations."
The BBC's Katy Watson in Washington says there is a feeling that the relationship between Iran and the US could move forward after years of stalemate.
The 64-year-old former nuclear negotiator added that no country could preserve peace by waging war, and said Iran would not cause conflict with any other nation.
He also nominated a cabinet that included moderates in key positions, including ex-UN envoy Mohammad Javad Zarif as foreign minister.
However, he did not mention the nuclear programme, which has blighted Iran's international relations and seen a slew of economic sanctions.
Iran has consistently said its programme is aimed only at providing power and has no military objective.
But UN inspectors have regularly complained of being denied access to the most suspect nuclear sites.
White House spokesman Jay Carney said Mr Rouhani's inauguration "presents an opportunity for Iran to act quickly to resolve the international community's deep concerns over Iran's nuclear programme".
"Should this new government choose to engage substantively and seriously to meet its international obligations and find a peaceful solution to this issue, it will find a willing partner in the United States," he said.
Mr Rouhani, who has worked as a diplomat for three decades, won a surprise victory in June's election.
He gained support from reformists by hinting at a more moderate stance than his predecessor.