Security forces clashed with protesters near Pakistan's parliament on Tuesday as hundreds of supporters of jailed former Prime Minister Imran Khan demanded his release in demonstrations the government said have killed four paramilitary troops.

Supporters of the ex-prime minister marched toward Islamabad, the capital. Clashes with the police left at least one officer dead, the authorities said.

Pakistan's capital, Islamabad, is under lockdown for a second day as thousands of protesters demanding the release of former prime minister Imran Khan from jail converge on the city. His supporters are also calling for the overturning of election results they say were rigged - a claim disputed by the government.