ISLAMABAD, Pakistan — Thousands of supporters of a firebrand Pakistani cleric, many armed with sticks and iron rods, have blocked a main entrance to Islamabad since last week, demanding the resignation of the country’s law minister and a strict adherence to blasphemy laws.

Led by Khadim Hussain Rizvi of the Tehreek-e-Labaik Pakistan party, at least 3,000 protesters were staging a sit-in on one of the main highways leading to the capital.

Officials say they suspect some of the protesters are carrying more serious weapons, and there is concern the standoff might turn violent. In response, the government has blocked several other roads to stop the protesters from moving to important government buildings.

Crippling, hourslong traffic jams have resulted. Long lines of vehicles could be seen for much of the past week and on Sunday on the roads leading to Islamabad from the suburbs and neighboring Rawalpindi. Several schools near the protest site remained closed. Shipping containers barricading the main streets are a ubiquitous sight.