At least three people were killed and nearly 400 admitted to hospitals, officials said, in clashes that started Saturday night and continued to boil over Sunday.
Prime Minister Nawaz Sharif met with top advisers seeking a way to ease the violence, which has raised the stakes in the two-week sit-in led by opposition politician Imran Khan and fiery cleric Tahir-ul-Qadri. They want the prime minister to step down over their allegations of massive voting fraud in the election that brought him into office last year in the country's first democratic transfer of power.
Sharif's party was elected in a landslide in which observers found no evidence of widespread fraud. The prime minister has refused to step down, and negotiators have tried to convince Qadri and Khan to end their protests.
The military weighed in after a late Sunday meeting, saying that it had "serious concern" about the crisis and the "violent turn it has taken."