Thousands of supporters of jailed former Prime Minister Imran Khan defied a government lockdown and violent police opposition to march to the outskirts of Islamabad, Pakistan, on Monday evening and demand his release, the latest escalation of political tensions.

At least one officer was killed, and several officers and demonstrators were injured, the government said.

Mr. Khan, who has been in jail since August of 2023 and faces more than 150 criminal cases, remains hugely popular despite attempts by the military-backed civilian government to suppress his support. His party, Pakistan Tehreek-e-Insaf, or P.T.I., says the cases are politically motivated.

Mr. Khan accuses the government and military of teaming up to crush his party, rig elections and undermine democracy. The government argues that Mr. Khan is sowing chaos through protests and insists the charges are legitimate, framing him as someone who refuses to play by the rules. It has rejected Mr. Khan’s calls to negotiate for his release.

On Sunday, Mr. Khan strongly urged his supporters to descend on the capital, demand his release, call for fresh elections and reverse constitutional amendments that have curtailed judicial powers.

The police said thousands of supporters, led by Mr. Khan’s wife, Bushra Bibi, and key aide Ali Amin Gandapur, who is also the chief minister of northwestern Khyber Pakhtunkhwa province and has led previous protests, set off from Peshawar on Sunday. Along the way, they removed shipping containers and barriers as the police deployed tear gas in the Attock district, about 50 miles from Islamabad. Officials said one police official was killed in clashes on Monday.