PESHAWAR, Pakistan - - The main supply route for NATO troops in Afghanistan was temporarily closed on Sunday after thousands of people blocked a key highway in Pakistan to protest against U.S. drone strikes, officials said.

Pakistani cricket legend-turned politician Imran Khan addresses the crowd during a rally against the U.S. drone strikes in Pakistani tribal areas, Saturday, April 23, 2011, in Peshawar, Pakistan. Pakistan stopped NATO supplies from traveling to Afghanistan on Saturday as thousands of protesters rallied on the main road leading to the border, demanding U.S. Washington stop firing missiles inside the country. (AP Photo/Mohammad Sajjad) The NATO-led International Security Assistance Force (ISAF) in Kabul, however, said the two-day blockade would have no impact on the alliance's operations in Afghanistan.

"Coordination with Pakistani government officials has been conducted and we understand the government will maintain security," an ISAF spokesman said. "There is no impact on ISAF sustainment."

The routes through Pakistan bring in 40 percent of supplies for NATO forces in Afghanistan, according to the United States Transportation Command. Of the remainder, 40 percent come through Afghanistan's neighbors in the north and 20 percent by air.

The call for blocking the supply line came from cricket-turn-politician Imran Khan after U.S. officials rejected Pakistan's demand for sharp cuts in drone strikes in its tribal regions where al Qaeda and Taliban militants are based.

Activists from Pakistan Tehrik-e-Insaaf (PTI), Khan's party, and some Islamist parties staged a sit-in on the highway leading to Afghanistan through the Pashtun tribal region of Khyber.

"It is meant to send a message outside that we oppose drone strikes. We will never accept them," Asad Qaiser, PTI president in the northwestern Khyber Pakhtunkhwa province, said.

The supply to Afghanistan through Khyber region had been suspended since the protest started on Saturday, a senior provincial government official, Siraj Ahmed, said.

The Chaman border crossing in the southwest has remained open to traffic, another official said.

The attacks by U.S. pilotless aircraft are a source of concern for the Pakistani government, which says civilian casualties stoke public anger and bolster support for the Islamist militancy.

But the protests have irked Pakistani truckers involved in the lucrative business of transporting supplies to the foreign troops in Afghanistan.

"They are politicians. They keep doing such dramas. But we cannot take risk so it is better to keep our trucks off the road for a few days," Mohammad Shakir Afridi, the president of Khyber Transport Association, said.

"We are fed up with this business," he added. "Every second day either trucks are attacked or the supply to Afghanistan is suspended. We say if you (the government) do not want it, cut it off permanently or provide us proper security."

He said his truckers had taken advanced payment for the shipments and if they don't go through, they would have to pay back that money.

"We have been trapped in a quagmire," Afridi said.

(Additional reporting and Writing by Kamran Haider, Editing by Chris Allbritton and Sanjeev Miglani)