(AP) -- NATO forces in Afghanistan are stepping up pressure on insurgents in the Taliban heartland of Kandahar.

A NATO spokesman says the combat phase of "Operation Dragon Strike" is under way. He describes it as "a significant ground operation with air support," and says the fighting is expected to be heavy.

The joint military push with Afghan forces around Kandahar City is intended to rid the area of insurgents and interrupt their ability to move freely and stage attacks.

The push in Kandahar is seen as key to the Obama administration's strategy to turn around the nine-year war. Seven U.S. troops have been killed in Kandahar this month.

On another front, NATO says more than 30 insurgents were killed when it launched an airstrike on Friday after a cross-border attack on an Afghan National Security Force outpost in Khost (hohst) province, near Pakistan.

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