The intervention was the latest chapter in a saga that began Saturday, when thousands of protesters led by Pakistani politician and cricket star Imran Khan blocked a road in northwestern Khyber Pakhtunkhwa province, which is used to ship goods to and from Afghanistan.
Khan's party, Pakistan Tehreek-e-Insaf, said they would block NATO shipments until the U.S. ended drone attacks.
On Sunday, members of Khan's party stopped trucks and roughed up drivers ferrying NATO supplies at a toll booth on the outskirts of Peshawar, Khyber Pakhtunkhwa's provincial capital. Police were present at the scene Sunday but did not stop the protesters, some of whom were carrying wooden batons.
Police officer Behram Khan said Monday that police would permit peaceful protests on the roadside, but activists would not be allowed to stop trucks as they did before. Police also opened an investigation into the activists' actions that could lead to legal charges, he said.
Covert CIA drone strikes targeting Islamic militants in Pakistan's northwest have long been a sensitive subject, with officials regularly criticizing them in public as a violation of the country's sovereignty. The issue is more complicated, however, since the
government is known to have supported at least some of the attacks in the past.
Imran Khan, whose party runs the Khyber Pakhtunkhwa government, has been a vocal critic of the strikes. The route blocked by his activists leads to one of two crossings used by trucks to carry NATO troop supplies and equipment to and from Afghanistan. The other crossing is in southwest Baluchistan province and has not been affected by the protest.
The federal government has also criticized drone strikes but has indicated it has no interest in blocking the NATO supply route, which could spark a crisis with the U.S. and other NATO countries. The police actions Monday indicated that the federal government had intervened to stop the NATO blockade.
The provincial police chief in Khyber Pakhtunkhwa, Nasir Durrani, ordered police to prevent protesters from stopping trucks and open an investigation into those activists who were halting vehicles on Sunday, said a statement from the police chief's office.
Although the police chief works with the provincial government, he is ultimately accountable to the federal interior minister, giving the federal government significant control.
The land routes through Pakistan have been key to getting supplies to NATO troops in Afghanistan. They now increasingly are being used to ship equipment out of Afghanistan as the U.S. seeks to withdraw most of its combat troops from the country by the end of 2014.
The routes have been closed in the past. The Pakistani government blocked the routes for seven months following U.S. airstrikes that accidentally killed two dozen soldiers on the Afghan border in November 2011. Pakistan finally reopened the routes after the U.S. apologized.