Pakistan police said Wednesday they had arrested nearly 1,000 protesters who marched on the capital demanding the release of jailed ex-prime minister Imran Khan, after crowds were evicted from the city centre in a sweeping security crackdown.

Thousands of supporters of Pakistan’s jailed former Prime Minister Imran Khan broke through barricades around the capital Tuesday and marched into Islamabad, clashing with security forces and demanding his release.

The crackdown brought a swift end to the protests that have gripped Islamabad, Pakistan’s capital, this week ever since thousands of people gathered in the city to demand the release of Imran Khan, the former prime minister. Mr. Khan has been in prison since last August on charges that his party claims are politically motivated.