Hundreds of Iraqi men trying to flee the fighting on Fallujah are being turned back by US troops who are under orders to allow only women, children and the elderly to leave.
The US military says it has received reports warning that insurgents will drop their weapons and mingle with refugees to avoid being killed or captured by advancing American troops.
As it believes many of Fallujah's men are guerrilla fighters, it has instructed US troops to turn back all males aged 15 to 55.
"We assume they'll go home and just wait out the storm or find a place that's safe," said one officer. "There is nothing that distinguishes an insurgent from a civilian. . . . If they're not carrying a weapon, you can't tell who's who."
Colonel Michael Formica, who leads forces isolating Fallujah, admits the rule sounds "callous" but insisted it is is key to the mission's success.
Troops have cut off all roads and bridges leading out of the city. Relatively few residents have sought to get through, but officers here say they fear a larger exodus.
Once the battle ends, military officials have said all surviving military-age men can expect to be tested for explosive residue, catalogued, checked against "insurgent" databases and interrogated about ties with the guerrillas.
US and Iraqi troops are searching homes and plan to check every house in the city for weapons.
AP