Thousands of Imran Khan supporters marched closer to the capital of Islamabad on Monday demanding his release from prison as authorities braced to prevent the crowd from entering the city.

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.

At least one policeman was killed and dozens on both sides wounded as supporters of jailed former Prime Minister Imran Khan clashed with security forces outside Pakistan's capital Islamabad on Monday,