A one-day ban on automobile traffic in the Baghdad region has imposed an eerie quiet on the Iraqi capital.
During Friday prayers, most religious leaders called for calm. But a Sunni sheikh, Ahmed Hassan al-Taha in Samarra, the site of February's bombing of a Shi'ite shrine, has blamed the latest sectarian violence on outsiders.
Prime Minister Ibrahim al-Jaafari had appealed to the nation's clerics to avoid inflammatory language during Muslim prayers.
Meanwhile, the U.S. commander in Iraq said on Friday the latest crisis appears to have passed, but another major attack on a religious site could have a negative impact.
General Casey praised Iraq's government and security forces for taking the lead in combating the recent violence, but he said they had allowed Shi'ite militias through some security checkpoints.
General Casey said the Iraqi government should focus now on gaining control of private militias.
He spoke to Pentagon reporters via video conference from Iraq.
Before today's traffic ban went into effect, gunmen killed at least 18 Shi'ite workers in a small town near Baghdad.
Meanwhile, a coalition of Sunni and Kurdish politicians has called on Iraq's Shi'ite prime minister to step down.
The politicians say Ibrahim al-Jaafari is an obstacle to political unity, but a spokesman for the Shi'ite bloc says it continues to back him for another term as prime minister.
The political jockeying comes as some Sunni leaders blame the Shi'ite-led government for failing to stop continuing violence in the war-torn country.
Iraq's political factions have been meeting to try and form a unity government.