ISLAMABAD — Opposition supporters in Pakistan have temporarily called off protests demanding the release of jailed former prime minister Imran Khan, a day after marching on central Islamabad.

Protesters had vowed not to leave the capital until Khan's release. But as they breached barriers and made their way to Democracy Square on Tuesday, they were pushed back by police and were met with volleys of tear gas.

At least six people - four security officers and two civilians - died in clashes during the latest protests, which began on Sunday.

Khan's party, Pakistan Tehreek-e-Insaf (PTI), said in a statement on Wednesday that the protests had been "temporarily suspended" due to the "government's brutality".

The crackdown on the protestors was swift. Although Khan’s supporters had managed to reach the centre of the city, by sunset on Tuesday the authorities had dispersed them.

One government source told local media that the police had arrested more than 500 PTI supporters and the interior minister said that his wife Bushra Bibi, who had been central to the protest, had left the area.

The PTI have claimed that several of their party workers were killed during the crackdown and appealed for an investigation.

Overnight the BBC spoke to two sources at a nearby hospital who said that they had received four bodies of civilians with gunshot wounds.

The BBC has not yet independently verified the reports. Pakistan's information minister said the authorities had resisted firing on protesters.

Islamabad had been put under lockdown, with a heavy security presence deployed in anticipation of clashes with convoys of PTI supporters.

The convoys were led by PTI leader Ali Amin Gandapur and Khan’s wife Bushra Bibi, who was released from prison in October and has since taken a more prominent role in trying to mobilise support for Khan.

Reports say Gandapur and Bushra Bibi have left Islamabad and returned to Khyber Pakhtunkhwa province, where their convoy had come from.

Protesters were reported to have responded to a “final” call from Khan, asking them to “fight till the end” until their demands are met.

Their destination was D-Chowk near central government buildings in Islamabad, and the site of political rallies and protests since the 1980s.

But only some of the protesters made it that far.

By Tuesday evening - just hours after protesters first reached the square - security officers had successfully cleared the area. As darkness fell, the lights were switched off - with only police officers and paramilitary soldiers left behind.

Khan has been in prison for more than a year on charges he says are politically motivated.

Even from behind bars, the former cricket star has proved a powerful player in Pakistan politics. During elections in February his 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 a majority and their rivals united to form a new government.

The PTI has called for election results to be overturned because they say the vote was rigged, a claim disputed by the government. — BBC