The Pakistani military has blocked a convoy carrying thousands of Pakistanis and a small contingent of US anti-war activists from entering a lawless tribal region along the border with Afghanistan to stage a protest against American drone strikes.
The group, led by cricket star turned politician Imran Khan and his political party, was turned back just miles from the border of South Waziristan.
After an hour of fruitless negotiations, Mr Khan announced that the caravan would backtrack to the city of Tank, about nine miles away, where he was expected to make a speech to the crowd.
Mr Khan has harshly criticised the Pakistani government's cooperation with Washington in the fight against Islamist militants.
He has been especially outspoken against US drone strikes targeting militants and has argued that the country's alliance with Washington is the main reason Pakistan is facing a homegrown Taliban insurgency.
He has suggested before that militant activity in Pakistan's tribal areas will dissipate when the US ends the war across the border in Afghanistan.
Pakistan's tribal regions, such as North and South Waziristan, border Afghanistan and serve as bases for militant groups such as the Taliban to stage raids across the border into Afghanistan.
Thousands of supporters had turned out along the route to cheer on the convoy, which stretches about nine miles including accompanying media. Some of those packed into the vehicles waved flags for Mr Khan's political group and chanted: "We want peace."
Video on Pakistani media showed barricades with hundreds of police in riot gear, a sign of concerns that the motorcade would be attacked or become unruly.
Around three dozen Americans from the US-based anti-war group CODEPINK joined Mr Khan for the march. The American protesters say the US drone strikes, contrary to the claims of American officials, have terrorised peaceful tribes living along the border and killed many innocent civilians - not just Taliban and al Qaida fighters.