Iran is "ready to assist Iraq" in its fight against Sunni insurgents, Iran's President Hassan Rouhani said.
In a televised statement, Rouhani said Iran would "strongly defend its territory if terrorist groups endanger its security."
He said Iran stands ready to help Iraq within the framework of international law, but added Baghdad has not requested assistance.
Islamist militant group ISIS stormed several northern Iraqi cities, forcing hundreds of thousands to flee into Kurdish-controlled territory.
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."