Ousted Pakistani Prime Minister Nawaz Sharif and his daughter Maryam, both facing lengthy prison terms, were arrested minutes after landing in the country as they returned seeking to revitalise their flagging party ahead of a July 25 election.
Underscoring the tensions gripping Pakistan in the run-up to the poll, a suicide bomber had killed more than 100 people at an election rally a few hours earlier, in the deadliest such attack in the country in more than three years.
"I'm aware of the fact that I'll be jailed, but it's a very small price to pay for the great mission to save the sanctity of the vote in Pakistan," Sharif told Reuters on board the plane minutes before touching down in the central city of Lahore.
Uniformed men escorted the Sharifs, who were sentenced in absentia on corruption charges last week, off the commercial flight, and a spokesman for their Pakistan Muslim League-Nawaz (PML-N) party confirmed they were arrested soon afterwards.
Their return represents a high-stakes gamble, but could shake up an election race riven by accusations Pakistan's powerful military is working behind the scenes to skew the contest in favour of ex-cricket hero Imran Khan. He describes Sharif as a "criminal" who deserves no support.
Clashes broke out on Friday evening at the main highway entry point to Lahore between pro-Sharif protesters and police who had been deployed in their thousands, a Reuters witness said. There were no immediate reports of injuries.
The security situation has improved in recent years in nuclear-armed Pakistan, but the substantial threat still posed by militants was starkly illustrated by the attack on an election rally of a regional party in Baluchistan province, in southwestern Pakistan, that killed 128 people.
The bombing was the third incident of election-related violence this week.
After their arrest at the airport in Lahore, Sharif and his daughter were immediately put on another plane and flown to the capital Islamabad, PML-N media coordinator Muhammad Mehdi said. Local media said they were then taken to Adiala jail in the nearby garrison town of Rawalpindi.
Their swift departure prevented PML-N workers staging a hero's welcome on the streets of Lahore, where Sharif's brother, Shehbaz, led between 10,000 and 20,000 party supporters on a march in defiance off a citywide ban on public gatherings ordered by the caretaker government that took over in June, as Pakistan's constitution requires in the lead-in to an election.
Pakistan's third major political movement, the Pakistan Peoples Party, joined the criticism of the crackdown, with its prime ministerial candidate Bilawal Bhutto Zardari questioning why Sharif's supporters would be prevented from gathering.
"Why is Lahore under siege? Right to peaceful protest is fundamental for democracy," tweeted Bhutto Zardari, the son of two-time prime minister Benazir Bhutto, who was assassinated at a political rally in 2007.
The country's media regulator warned local news channels to abstain from airing statements "by political leadership containing defamatory and derogatory content targeting various state institutions specifically judiciary and armed forces", the regulator said in a statement.