A handful of Sunni mosques were attacked or burned Thursday, but curfews and increased troop levels kept Iraq in relative calm a day after suspected al-Qaida bombers toppled the towering minarets of a prized Shi'ite shrine. The US military issued a statement Thursday saying Iraqi forces had arrested the Emergency Service Unit commander and 12 policemen responsible for security at the shrine at the time of the explosions. "We must condemn the bad actions of terrorists, and the sons of all tribes must come together and forgive each other," the military quoted Brig.-Gen. Duraid Ali Ahmed Mohammad Azzawi, deputy commander for the National Police in Samarra, as saying. Increased US and Iraqi military patrols crisscrossed the streets of the Iraqi capital, and additional checkpoints were set up along roads leading to Sadr City, witnesses said. Hundreds of residents marched peacefully through the streets of that teeming neighborhood, a stronghold of Shi'ite cleric Muqtada al-Sadr's Mahdi Army. Demonstrations also took place in Kut, Diwaniyah, Najaf and Basra - all predominantly Shi'ite cities in the south. A ban on vehicular traffic was expected to remain in place in Baghdad until Saturday. Mid-afternoon, explosions rocked central Baghdad, and smoke billowed over the American-guarded Green Zone, which houses the US and British embassies, as well as the offices of the Iraqi government. A witness inside the zone, who spoke on condition of anonymity because of the sensitivity of his job, said about half a dozen mortar rounds fell in the area. The US military said it had no immediate information about the attack. An Associated Press reporter inside the zone said at least one rocket fell at the entrance to the Rasheed Hotel, about 150 meters (yards) from Iraq's parliament. Scattered, broken concrete littered the area. Several military and plainclothes officials were gathered around the impact site, wearing rubber gloves and sifting through rubble. There was no evidence of any casualties. Attacks on Sunni mosques began within hours of Wednesday's bombings in Samarra. Wednesday's attack on the Askariya shrine in Samarra, which was blamed on Sunni extremists, stoked fears of a surge in violence between Muslim sects. A bombing at the same mosque complex in February 2006 that destroyed the shrine's famed golden dome unleashed a bloodbath of reprisals. Police in the southern city of Basra said Thursday that four people were killed and six wounded in attacks on the Kawaz, Othman, al-Abayshi and Basra Grand mosques on Wednesday, all involving rocket-propelled grenades that also damaged the buildings. Basra is Iraq's second-largest city, 550 kilometers (340 miles) southeast of Baghdad. Four Sunni mosques near Baghdad also were attacked or burned within several hours of the Samarra bombings, police said. One of those mosques, which had been only partly destroyed, was a target again Thursday, police said. Around 4 a.m., attackers broke into the Hateen mosque in Iskandariyah, 50 kilometers (30 miles) south of Baghdad, and planted bombs inside. Flames from a huge explosion destroyed most of the building, and a woman and child in a nearby apartment were wounded, an Iskandariyah police officer said on condition of anonymity because he was not authorized to release the information. Gunmen also tried to storm the nearby al-Mustafa mosque early Thursday, and exchanged fire with guards before Iraqi soldiers arrived and stopped them, police said. There were no immediate reports of casualties. In Mahaweel, 56 kilometers (35 miles) south of Baghdad, gunmen opened fire on the al-Basheer mosque at dawn Thursday, police said. They forced guards to leave, then set fire to the mosque, a local police officer said on the same condition of anonymity. The building was partly damaged, he said. The Samarra site contains the tombs of the 10th and 11th imams - Ali al-Hadi, who died in 868, and his son Hassan al-Askari, who died in 874. Both are descendants of the Prophet Muhammad, and Shi'ites consider them to be among his successors. Also Thursday, the US military said it detained 25 suspects in raids against al-Qaida in Iraq over the past two days. One taken into custody near Tarmiyah, 50 kilometers (30 miles) north of Baghdad, was believed to be a close associate of Omar al-Baghdadi, who heads the al-Qaida front group Islamic State in Iraq.