Two gunbattles in eastern Afghanistan killed four Afghan and two U.S. troops, officials said Tuesday, and NATO prepared to assume military command of all of the country from the U.S.-led coalition.

A suicide bomber on a motorbike attacked a Canadian military convoy in the city of Kandahar, but no troops were injured, said Maj. Daryl Morrell, a spokesman for the NATO-led force.

Two American and one Afghan soldier died Monday during a gunfight with militants in eastern Kunar province, which borders Pakistan, the U.S. military said. Three U.S. soldiers were wounded in the battle in Pech district, it said.

"The soldiers were operating as part of a combat patrol that made contact with enemy extremists. The unit engaged the insurgents with small arms and artillery fire," the statement said.

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About 7,000 Afghan and U.S. troops are operating in eastern Afghanistan as part of Operation Mountain Fury, aimed at wiping out militants and extending the Afghan government's reach.

Separately, three border police were killed and three wounded late Monday after Taliban fighters attacked their outpost near the border in the eastern province of Paktika, said provincial Gov. Mohammad Akram Akhpelwak.

In the Taliban's former southern stronghold of Kandahar, flames engulfed a military vehicle after a suicide bomber rammed into a NATO convoy, witnesses said.

"I was sitting outside my shop. I saw a motorbike come close to the Canadian convoy, and then (the driver) detonated himself," said a witness, Ali Ahmad.

NATO-led troops, meanwhile, will take over the command of military operations for all of Afghanistan from the U.S.-led coalition on Thursday, said Daan Everts, the alliance's senior civilian representative in Afghanistan.

The takeover is seen as a significant step in an already historic expansion of missions for the largely European alliance that was created as a Cold War bulwark against the Soviet Union.

Of the 40,000 foreign troops in Afghanistan, about 8,000 U.S. troops tracking Al Qaeda terrorists or involved in air operations will remain outside NATO's control, officials said.

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NATO's twin roles of combating the growing violence and trying to extend the reach of the Afghan government are among the most challenging missions the alliance has undertaken in its 57-year history.

Afghanistan in recent months has seen the largest increase in violence since the U.S.-led invasion ousted the Taliban regime in 2001.

A suicide bomber in the capital, Kabul, killed 12 people and wounded more than 40 on Saturday.