NATO is rejecting claims by Afghan residents that several civilians were killed during an air raid in southern Helmand province.

In a statement Tuesday, NATO said it killed an estimated 12 insurgents in an isolated area of Helmand's Sangin district Monday. NATO said it attacked after militants riding in three vehicles fired on coalition forces.

NATO said there was no evidence of civilian casualties.

Local lawmakers and Sangin residents said at least 50 people were killed when NATO jets bombed an area where people were playing games.

They said at least half the victims were civilians.

U.S., NATO and Afghan forces are struggling to contain a bloody Taliban insurgency in the southern and eastern parts of Afghanistan.

This week, more U.S. Marines began arriving in southern Afghanistan to help fight insurgent attacks.

They were deployed after Canada threatened to remove its forces from Afghanistan unless NATO sent a 1,000 more troops.

The Canadian parliament said last week that if more troops were sent, it would extend the country's presence in Afghanistan through 2011.

In response, the United States assigned 3,200 Marines to a seven-month-long mission in Kandahar province, a Taliban stronghold.