Pakistani officials say unidentified gunmen in central and northwestern parts of the country have set fire to at least seven tankers carrying fuel for foreign troops in neighboring Afghanistan.

The officials say that late Monday, an explosion at a terminal at the Torkham border crossing in the northwest destroyed at least three tankers. Minutes later, in the same area, two more NATO tankers were damaged when the gunmen opened fire at them.

After a separate attack near Multan, four oil tankers were burning late Monday.

Last week, the Pakistan Oil Tankers Owners Association demanded more protection from the government. The group threatened Friday to stop supplying NATO within 24 hours if the government fails to act.

The bulk of fuel and other non-lethal supplies for NATO troops in Afghanistan moves through Pakistan.