Shakil Adil / AP A Pakistani man walks by a truck carrying NATO military vehicles at a terminal in Karachi, Pakistan, Tuesday, Nov. 26, 2013

Washington has temporarily halted military supplies moving by ground out of Afghanistan along a key route through Pakistan, according to news agencies, citing safety concerns for its truck drivers.

Activists have been staging protests along key NATO supply routes in Pakistan since November, after a drone strike killed the leader of the Pakistani Taliban shortly before peace talks between the militant group and the government began. Some protestors have been detained for allegedly harassing truck drivers, according to reports.

Cricketer-turned-politician Imran Khan, head of the Pakistan Tehreek-e-Insaf (PTI) party, has been leading the protests in Khyber Pakhtunkhwa province, where his party is in power. On Dec. 3, Khan told the Express Tribune that PTI is also considering blocking supply routes that run through Punjab province and Balochistan.

At present, 60% of NATO supplies leaving Afghanistan ahead of next year’s troop withdrawal are moved by ground through Pakistan, according to the International Security Assistance Force (ISAF). Other ways to move shipments out, through Central Asia or by air, are more expensive.