Police officer Muhammed Akram said that security forces used blockades and tear gas but could not disperse the crowd, who gathered in the garrison city of Rawalpindi and then marched to Islamabad.
The protesters were marching against the hanging of Mumtaz Qadri in February. Qadri was charged for the 2011 murder of governor Salman Taseer, who was defending a Christian woman jailed on blasphemy charges.
Another police officer, Muhammad Nasim, said that the march of around ten thousand people was peaceful initially, but as the crowds reached an avenue leading to parliament the protesters turned violent, smashing windows and damaging bus stations.
Malik Ahsan, a doctor at Islamabad's main hospital, said that 13 people were wounded in the demonstration. Most of them were police officers admitted to hospital after having been hit with stones.
Police used tear gas in an abortive attempt to stop the unruly crowd as they approached parliament. People in offices close to the parliament building said they were affected by the gas. Witnesses said that protesters torched police barricades and lit fire to bushes.
The protest leaders, speaking from a truck close to parliament, called on demonstrators not to be scared and to advance on the government building, but the crowd thinned. The leaders said they would hold a sit-in until their demands are met, but did not specify what their demands are.
The army was called in to control the situation and stationed troops outside parliament, army spokesman Maj.Gen Asim Salim Bajwa said
Related story
NRB Governor Paudel assigns portfolios to deputy governors
