Iran could cooperate with the United States in fighting "terrorist groups in Iraq and elsewhere," the country's President Hassan Rouhani said.
"We all should practically and verbally confront terrorist groups," Rouhani told a press conference broadcast live on state television.
The relationship between the the US and Iran have been very cold for decades. The US has imposed tough sanctions on Iran in the past, accusing it of sponsoring terrorism and violating nuclear weapons rules.
The links have improved slightly since the election of Mr Rouhani in 2013.
Shi'ite Muslim Iran is alarmed by the Sunni insurgence in the north of Iraq.
The Foreign Secretary has been clear on the threat of Isis, but he has ruled out the prospect of any UK military involvement in the crisis.
Iraq’s foreign minister, Hoshyar Zebari, is a natural diplomat. Polite, immaculately dressed, and blessed with a great memory.
Isis has paraded military equipment in Mosul it captured from when the Iraqi army fled in what some see as a "nightmare scenario."