A magnetic bomb placed on a truck exploded and destroyed 21 other trucks transporting supplies and fuel for NATO's U.S.-led occupation of Afghanistan early Wednesday morning, local officials report. Taliban insurgents attacked the convoy in a previously secure northern region, authorities said.

Afghan firefighters spray water on burning NATO supply trucks in Samangan province on Wednesday. (Reuters) The truck convoy had been parked overnight in the northern Afghan province of Samangan after crossing from Uzbekistan.

The Washington Post reports that Samangan straddles a highway that has been used in recent months as the key overland supply line for foreign forces after Pakistan barred NATO supply convoys from its territory as a protest over the killing of 24 Pakistani troops in a U.S. air attack on two border outposts in November. Although Islamabad has lifted the blockade in recent weeks, foreign troops still rely on the northern Afghan region as a route for supplies from Central Asia.

NATO’s International Security Assistance Force (ISAF) spokesman Brigadier General Gunter Katz said insurgent attacks have been increasing.

“Generally, in the past 12 weeks, we have a slight increase, 10 per cent, of insurgent attacks on Afghan security forces and international troops,” Katz told a news conference.

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Burning NATO supply trucks are seen in Samangan, north of Kabul, Afghanistan, on July 18, 2012. Afghan officials say a magnetic bomb placed on a truck exploded and destroyed 22 NATO supply vehicles. (Javed Basharat/AP)

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