NATO commanders called on the Taliban to surrender as troops dug in on Monday for a major assault on one of the last insurgent strongholds in southern Afghanistan. The Taliban remained defiant as civilians of the Marjah plain accused the militia of massing fighters and arms for a bloody battle in Helmand province expected to start this week. Thousands of residents have fled the area. Yousuf Ahmadi, a purported Taliban spokesman, told AFP by telephone that Taliban fighters prefer to stay and fight. Brigadier General Eric Tremblay, spokesman for NATO's International Security Assistance Force, called on the militants to lay down their arms, and said the aim of the operation is to separate the insurgents from the population. A stream of frightened families are packing up their belongings and leaving Marjah, as provincial authorities set up emergency reception centres and stockpiled food and tents for up to 10,000 people.