ISLAMABAD, Pakistan — Thousands of Pakistani police officers in riot gear fired tear gas and rubber bullets on Saturday as they tried to clear out supporters of a firebrand cleric who have paralyzed the Pakistani capital for weeks with a protest on a main highway.

Authorities said at least six protesters were killed and 200 people — including dozens of police officers and paramilitary troops — were injured as stone-throwing crowds fought with police for control of a highway intersection. Clashes also broke out in other cities, including Lahore and Karachi, with officials saying at least 150 protesters have been arrested.

As plumes of smoke rose from the site of the highway clashes, officials in Islamabad requested the help of the Army to “control the law-and-order situation” in the capital, according the Ministry of Interior. The ministry said that the military authorities would determine the number of troops to be deployed.

The demonstrations began three weeks ago after the release of a proposed new version of an oath to be taken by lawmakers that omitted mention of the Prophet Muhammad. The protesters, many of them supporters of the cleric, Khadim Hussain Rizvi, an outspoken Islamist, have demanded that the law minister resign for the omission, which they called blasphemy.