Islamabad: Pakistan Army has been pressed in to control the situation as thousands protesting the execution of Mumtaz Qadri - a former Punjab police commando hanged last month for assassinating Punjab governor Salman Taseer - breached Islamabad's Red Zone on Sunday evening.
The government has called in the army to control the law and order situation.
Protesters removed containers and blockades on the way to the Parliament House and also set some containers to fire before staging a sit-in outside the building, where fiery anti-government speeches are being delivered, Dawn reported.
Earlier in the day, riot police used tear gas and batons to disperse the stone-pelting crowd from the high-security zone outside the parliament building.
More than 25,000 people had gathered in Rawalpindi`s Liaquat Bagh on Sunday to participate in the Chehlum of Qadri.
The crowd then turned towards the heavily-barricaded capital city, which was patrolled by hundreds of police and paramilitary soldiers. Several major arteries leading to Islamabad were closed by authorities to block the crowd`s route.
The protest was almost entirely ignored by the media, which has increasingly become subject to government-ordered news blackouts designed to prevent unrest from spiralling out of control.
Qadri was a bodyguard of Punjab Governor Salmaan Taseer when he shot him 29 times in 2011 over his call to reform the blasphemy law, which critics say was frequently misused to oppress religious minorities.
Blasphemy is a hugely sensitive issue in Pakistan, where even unproven allegations can stir mob violence and lynchings.