Pakistani security forces pushed a protester off a 25-foot tall stack of shipping containers as they were accused of opening fire on supporters of Imran Khan at a huge demonstration in Islamabad.

Supporters seeking the release of imprisoned Pakistani former Prime Minister Imran Khan broke through a ring of shipping containers blocking off the capital on Tuesday, and battled security forces despite a government threat to respond with gunfire.

Police in Pakistan clashed with thousands of Imran Khan supporters as they marched towards the capital Islamabad to demand his release, defying a lockdown and a ban on rallies. The former Pakistani prime minister has been in jail for over a year on more than 150 criminal charges.