(Updates with NATO firing on Afghan civilian, background)

KABUL, July 2 (Reuters) - Seven Afghan policemen were killed when a roadside bomb hit their vehicle outside the southern city of Kandahar on Monday, police said.

Police chief Sayed Agha Saqib said the vehicle was hit by a remote-controlled bomb.

"It is a powerful explosion. It was carried out by enemies of Afghanistan," he said.

Violence has surged in the past 17 months in Afghanistan, the bloodiest period since U.S.-led troops overthrew Taliban's government in 2001.

Taking a lead from the Iraq insurgency, the Taliban have increasingly resorted to suicide and roadside bomb attacks against foreign troops or Afghan government targets.

Separately on Monday, NATO soldiers in a convoy fired and wounded an Afghan on a motorbike in Kandahar City after he ignored warnings by the troops who mistook him for a suicide bomber, the alliance said.

"ISAF soldiers used hand signals to warn the man not to approach the convoy. Follow-on warnings included a flare and then four carefully aimed warning shots," said a statement from the NATO-led International Security Assistance Force (ISAF) for Afghanistan.

It said there were no other casualties, but local residents and a hospital official said one person was killed and four wounded in the firing.

"(The) Wounded told us that NATO forces opened fire on them without any reason," said Dr. Mohammed Hashim at Mirwais Hospital.

Taliban guerrillas have previously used motorbikes to carry out suicide attacks.

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