A Pakistani offensive against militants in the Swat Valley has displaced some 200,000 people and 300,000 are on the move or about to flee, the UN says.

As jets and helicopters pounded targets in the valley, the UN said it was threatening to become one of the world's biggest displacement crises.

Troops have killed more than 140 militants in the past 24 hours, army spokesman Gen Athar Abbas said.

He said that measures had been taken to provide for fleeing civilians.

But reports suggest some civilians are being prevented from leaving militant-held areas.

http://news.bbc.co.uk/2/hi/south_asia/8039767.stm