President Hassan Rowhani said Tuesday that Iran was ready for "serious" negotiations on its nuclear programme with the major powers "without wasting time".

"We are the people of interaction and talks, with seriousness and without wasting time, if the other sides are ready," he said at his first news conference since assuming office on Saturday.

"Iran's peaceful nuclear programme is a national issue... we will not give up the rights of the Iranian people," he said.

"We will preserve our rights based on the international regulations."

Rowhani also hit out a call by 76 US senators for tougher US sanctions even as he took office with a call for constructive engagement.

He said Friday's letter from the US lawmakers to President Barack Obama, which was published on Monday showed a lack of understanding of Iranian politics.

"We care about the US response in deeds, not in words," he said.