Thousands defy Pakistan police in support of Imran Khan

The city's roads have been blocked with shipping containers to stop the march reaching the centre

Thousands of opposition protesters have converged on Pakistan's heavily-barricaded capital, demanding the release of jailed former prime minister Imran Khan.

The convoy - which is aiming for a square in the centre of Islamabad - has already clashed with security forces, who have been firing tear gas and rubber bullets at the marchers in an attempt to disperse them.

According to the prime minister's office, four paramilitary soldiers have been killed in a hit-and-run, which it has blamed on Khan's supporters. This has not been independently verified.

Khan has been held in prison for more than a year, facing a slew of charges and sentences which he alleges are politically motivated.

Even from behind bars, the former cricket star has proved a powerful player in Pakistan politics. During elections in February, his Pakistan Tehreek-e-Insaf (PTI) party, which had been banned from standing and was forced to run candidates as independents, emerged as the single largest bloc.

However, they fell short of the majority and their rivals united to form a new government.

As a result, protesters are also calling for the overturning of election results they say were rigged - a claim disputed by the government.

It was Khan who called on his supporters to take to the streets at the weekend, issuing a "final call" and asking them to stay in the capital until their demands are met.

After days on the road, the protest has now reached D chowk, a large town square near the prime minister’s office, parliament, and Pakistan's Supreme Court.

"We are here only on Imran Khan's call, Imran Khan told us to come here, not for him, but for ours and our country's sakes," one protester told reporters on Tuesday, vowing to "stay here until Khan himself is here with us and tells us what to do next”.

The government - which had already introduced a ban on public gatherings -responded by blocking Islamabad's streets with shipping containers, and bussing in police from across the country.

Restrictions also appear to have been brought in on some internet services, while schools and colleges have been shut because of fears of violence.

Pakistan's interior minister said the protesters had been offered an alternative venue for their protest but had refused.

Prime Minister Shehbaz Sharif, who blamed the protesters for the deaths of the four soldiers on the protesters, dismissed the march as "extremism".

"These disruptive elements do not seek revolution but bloodshed," he said in a statement.