A suicide bomber struck the funeral of two anti-al-Qaida Sunni tribesmen in a town north of Baghdad on Thursday, killing at least 50 people and wounding dozens, police said. The blast was the latest this week to break a period of relative calm in Sunni areas, raising concerns that Sunni insurgents are reorganizing at a time when US and Iraqi troops are battling Shiite militiamen elsewhere. Over the past months, Sunni insurgent violence has eased with the increase in US troops and the growth of so-called Awakening Councils, groups of Sunni tribesmen and former insurgents who have joined American forces in fighting al-Qaida-linked militants. Thursday's attack took place in the town of Albu Mohammed about 150 kilometers north of Baghdad, during the funeral of two brothers who belonged to the local Awakening Council and had been killed in an attack a day earlier, police said. The suicide bomber walked into a tent crowded with mourners in the village and detonated explosives strapped to his body, police in the nearby city of Kirkuk said. Sheik Omar al-Azawi, a member of the local Awakening Council, was just pulling up at the tent in his car when the blast went off. "I first heard a thunderous explosion and when I turned my eyes to the tent I saw fire and smoke coming out," al-Azawi, 51, told The Associated Press in a telephone interview. "Panicked people were jumping and running on all sides, and then we started to evacuate those who were killed and wounded in our private cars until police and medical teams arrived," he said. He said the bomber, believed to be in his late 50s, was dressed in traditional Arab robes and that guards in charge of searching mourners allowed him in without a search. At least 50 people were killed and 50 injured in the blast, the police officials said, speaking on condition of anonymity because they are not authorized to talk to the media. The blast was the deadliest attack since March 6, when a bombing in central Baghdad killed 68. Thursday's attack came on the heels of a string of suicide attacks on Tuesday that killed 60 people in four major cities in central and northern Iraq. Also Thursday, gunmen in Baghdad killed two members of an Awakening Council in the Sunni district of Azamiyah and wounded a third, said Awas Mohammed, the spokesman for local Awakening Council. The US military has touted the relative calm in Sunni areas as a major success of the troop surge and the strategy of encouraging Awakening Councils and other Sunnis - some former insurgents - to turn against al-Qaida. US military spokesman Maj. Gen. Kevin Bergner said Wednesday that despite this week's stepped-up violence, the overall situation in Iraq has markedly improved over the past year. "We have said all along that there will be variants in which we will see al-Qaida and other groups seek to reassert themselves," Bergner said. But the new Sunni violence comes as fighting has increased between US-Iraqi forces and Shiite militiamen, particularly members of anti-US cleric Muqtada al-Sadr's Mahdi Army. In the early hours Thursday, a US drone fired rockets at gunmen in Baghdad's Sadr City district, the Mahdi Army's stronghold, which has seen near daily clashes recently. The US military said the strike killed two gunmen. Iraqi police said two civilians were killed and six others wounded, including a 9-year-old child in the strike, which they said damaged several apartments in the residential area. Thursday evening, two mortar shells landed in the Green Zone, the fortified Baghdad district where Iraqi government offices and the US Embassy are located _ the latest in nearly daily mortar volleys usually blamed on Mahdi Army fighters. There were no reports of casualties, the US Embassy said in a statement. An offensive launched on March 25 by Iraqi forces against Shiite militants in Basra touched off an uprising by Shiite militias across southern Iraq and in Sadr City. US officials have praised Prime Minister Nouri al-Maliki for the determination he showed in confronting the militias, but they have also said the Basra operation was hastily arranged and badly executed. Critics said it highlighted the Iraqi army's poor leadership and the low morale among its rank and file after some 1,000 troops deserted or refused to fight in Basra. Iraq's main Sunni Muslim political bloc agreed in principle to al-Maliki's Shiite-led government nearly nine months after quitting the Cabinet, lawmakers from the group said Thursday. A return of the Sunnis would be a boost to al-Maliki, who has struggled to keep together the disparate factions of his government and attempt to reconcile Iraq's feuding Shiite and Sunni politicians. Meanwhile, Baghdad and other parts of the country were blanketed by an all-day sandstorm that turned the sky yellow and sent dozens to hospital complaining of breathing difficulties.