The United States says it has agreed a ceasefire with the Iraq-based People's Mujahideen (MKO) - the main armed Iranian opposition group.
It says some of the group's fighters had moved into assembly areas in non-combat formation.
Iranian opposition in the US condemns Iran's attacks on the MKO
The MKO has maintained thousands of fighters along Iraq's border for many years.
Equipped by the Iraqi army, and sometimes used against the Iraqi population, it had been declared a terrorist organisation by Iran, the US and the European Union.
'Thorn in Iran's side'
The US-led coalition announced last week that it had been pounding MKO positions inside Iraq and that it was working to secure the group's surrender.
The coalition regarded the group as a legitimate military target because of its long-running links with President Saddam Hussein.
The MKO - a violent organisation with an ideology combining elements of Marxism and Islam - was driven out of Iran after the 1979 Islamic Revolution.
It set up bases in Iraq, using them as a springboard to launch attacks and assassinations on Iranian soil.
Tehran has already asked for any senior members of the group to be extradited if they are captured, and such requests are likely to be stepped up in the light of this ceasefire.
It is far from clear what might happen to anyone who surrenders, although the Iranian Government has said that rank-and-file members of the MKO could return home.
Tehran's top priority will be to ensure that the MKO - which has been a thorn in its side for two decades - is not allowed to regroup.