BAGHDAD, Iraq — Iraqi politicians allied with militant Shiite cleric Muqtada al-Sadr threatened Friday to resign from the government if Prime Minister Nouri al-Maliki meets next week with President Bush, adding to the pressure on an embattled premier who appears unable to halt his nation's plunge into full-fledged civil war.

Under curfew and under siege, Iraqi men and boys took up arms and stood watch with their neighbors after dark, anticipating attacks from the opposite sect of Islam. Mosques in at least one Sunni Muslim district of Baghdad ordered locals to fire on all strangers except for U.S. troops arriving to help protect them.

At least 55 people died Friday in Sunni-Shiite fighting and other violence, police and witnesses said, though that number was expected to rise as mortar attacks and other clashes continued late into the night. In Baghdad, bands of gunmen rampaged through a Sunni enclave in a predominantly Shiite district, killing some 30 people and torching several mosques and homes, police and witnesses said.

Wire services reported that Shiites burned six Sunni worshipers alive, but Iraqi security forces couldn't confirm the incident, saying the area was too dangerous for their patrols.

The Associated Press reported that Iraqi soldiers at a nearby army post failed to intervene as the Sunnis were seized as they left Friday prayers, drenched with kerosene and burned alive — or to stop subsequent attacks that killed at least 19 other Sunnis, including women and children, in the same neighborhood, the volatile Hurriyah district in northwest Baghdad, police Capt. Jamil Hussein said.

Bush aides in Washington said the meeting scheduled for Wednesday in neighboring Jordan would continue as planned, although al-Maliki's office hadn't issued a public response by midnight Friday in Baghdad.

Calls for a change in the Iraqi government echoed from mosques, political offices and funeral services as al-Maliki, a Shiite, faced a crucial test of his leadership and loyalties: Would he leave Iraq at such a volatile moment to meet with Bush, or stay and work with rival factions on a last-ditch effort to save his country from exploding?

Neither Iraq's political leaders, Iraqi government forces nor U.S. troops have been capable of securing the capital, despite curfews, increased checkpoints and more frequent patrols, and it isn't clear what could halt the escalating violence.

In the southern Shiite holy city of Najaf, funerals began for victims of car bombings that killed more than 200 people Thursday in Baghdad's Sadr City, a Shiite stronghold, in the deadliest violence since U.S.-led forces invaded Iraq in 2003.