The death toll from Saturday's assault on Camp Liberty, which houses about 3,000 members of the opposition People's Mujahedeen of Iran, meanwhile rose to seven, the group said.

Iraqi authorities are now investigating who was behind the attack, but the MEK and its supporters have called for the group to be allowed to return to their old base dating back to the 1980s -- Camp Ashraf near the Iranian border.

"The answer for the individuals at (Camp Liberty) is not to relocate back to Ashraf, in our view," State Department spokeswoman Victoria Nuland said.

"The only peaceful and durable solution for these individuals is resettlement outside Iraq, and that should continue to be the focus of everybody involved in this effort."

The residents were reluctantly and finally moved from Camp Ashraf last year, on Iraq's insistence, as part of deal negotiated via the United Nations.

They are now in the process of being resettled, and it is understood the United States and several European countries had agreed to take them in.

Nuland said the United States has still not made any decisions on whether to accept any of the residents.

"We are now in the process of evaluating some of the referrals that UNHCR has sent our way, and we're strongly, as I said, encouraging others to do the same," Nuland said.