BAGHDAD — At least five Sunni mosques in Iraq were attacked Thursday in apparent sectarian reprisals a day after the bombing of a revered Shiite shrine in Samarra.

But with U.S. and Iraqi troops — and Iraqi citizens — bracing for the possibility of ramped-up fighting between Sunnis and Shiites, most areas were reporting relative calm in the first hours after the Samarra attack.

The U.S. military said Wednesday that Iraqi security forces had arrested the Iraqi commander and 12 policemen from the unit that had been responsible for security at the shrine when it was attacked.

“We must condemn the bad actions of terrorists, and the sons of all tribes must come together and forgive each other,” Iraqi Brig. Gen. Duraid Ali Ahmed Mohammad Azzawi, deputy national police commander in Samarra, was quoted as saying in a U.S. military statement.

So far, it seems that the roughly 2 million residents of Sadr City, a huge Shiite slum in Baghdad and the power base of the Mahdi Army militia, have heeded calls for calm, according to U.S. military officials.

A protest involving roughly 2,000 people gathered in the Shiite district in Baghdad at about 10:15 a.m. on Thursday and dispersed a little over an hour later, according to Lt. Col. David Oclander, the executive officer of the 2nd Brigade Combat Team, 82nd Airborne Division.

“Muqtada al-Sadr has committed to three days of mourning and that will help ease the violence we would have seen,” Oclander said Thursday.

Oclander stressed that the curfew that has been indefinitely imposed was put in place by the Iraqi government.

“We are here to help enforce that, to lend a hand,” he said.

U.S. troops in the area are hoping to avoid a repeat of the violence that followed the bombing of the Askariya shrine last year when more than two dozen Sunni mosques in Baghdad were attacked in retaliation on the same day.

“We are on the lookout for large movements of military-age males,” Oclander said.

He added that U.S. military officials will also actively combat rumors sweeping through Sadr City and other sectors of the Shiite community that blame the United States as complicit in the destruction of the shrine.

“It’s just rumor and word-of-mouth-type stuff,” he said. “I do know we are going to get the record straight.”

On Wednesday, some leading Shiite clerics — and the Shiite president of Iran — blamed the U.S. military for not guarding the shrine more closely. The entire Iraqi police unit that was responsible for security at the site was detained for questioning, Iraqi officials said Wednesday.

Oclander said that U.S. troops as well as Iraqi security forces are keeping close tabs on the nearby Abu Hanifa Mosque in the predominately Sunni district of Adhamiyah in Baghdad.

“We haven’t seen any problems. We are engaging with the Iraqi security forces and we are going to engage with the local imam,” Oclander said.

Oclander said that, should violence erupt again, the U.S. military in Sadr City will be better prepared to respond. Since last year, his unit has carved out a presence in the southwestern corner of Sadr City, once a no-go zone for coalition forces.

From that foothold, “we can conduct operations anywhere in Sadr City,” he said.

He added, however, that he hopes calm can be maintained.

“If we can do it without firing a shot, we will,” he said.

In Babil province, south of Baghdad, U.S. Army officers with the 4th Brigade Combat Team, 25th Infantry Division are working with local Sunni and Shiite leaders, asking them to avoid attacks.

“We’re telling them to hold back, not to retaliate,” said Maj. Rick Williams, the brigade’s information operations officer, who also is in charge of tribal reconciliation.

But units remain on alert.

“It is volatile in our region, especially with the Sunni and Shia split,” said Maj. Eric Verzola, the brigade’s public information officer. He said the local media had reported five mosques hit in the unit’s area, “but we haven’t been able to confirm it yet.”

In Hillah on Thursday, Shiite residents led a demonstration in the provincial capital, but no violence was reported, Verzola said.

American units in Baqouba said most of volatile Diyala province had so far held.

“We keep driving on with the mission,” said Maj. Raul Marquez, 3rd Brigade, 1st Cavalry Division public affairs chief. “We haven’t seen any reactions from the people that tell us if something was going to happen.”

Diyala has been the scene of heavy fighting between U.S. forces and insurgents ever since President Bush announced he was sending more forces to Iraq to bolster security in Baghdad, the Iraqi capital.

The province is composed of about 50 percent Sunni Muslim, 33 percent Shia Muslim, 10 percent ethnic Kurds and 7 percent other ethnic and religious sects.

Marquez said senior brigade officers have been attentive to a possible surge in violence and have been talking with local Iraqi leaders, urging them to keep their people in line.

Stars and Stripes reporters Teri Weaver and Drew Brown contributed to this story.