The blast, in Syria's largest city, occurred near two hospitals. Some reports say both military personnel and civilians are among the victims.
A militant leader in Jordan, who has been linked to al-Qaida and several high-profile attacks, warned Syrian President Bashar Assad, 'our fighters are coming to get you.'
The State Department has said repeatedly that the Syrian Army is growing weak, but independent military analysts say it is still capable of handling the rebel forces.
The bombings, including one outside a mosque that killed the policemen, came as regime forces and rebels clashed in southern neighborhoods of Damascus.
President Assad's ground troops are nowhere to be seen in the rebel-held territory they call "Free Syria." But without a no-fly zone, civilians, like those today in Al-Bab, find themselves constantly vulnerable to aerial assaults.
Syrian civilians who have remained in Aleppo through weeks of fierce fighting face food and fuel shortages and live in fear of being killed while going about their daily tasks.
The waves of Syrian refugees seeking haven in Turkey and Jordan are testing the two countries, putting the oft-discussed idea of creating a 'safe zone' in Syria back on the table.
A Syrian army helicopter has crashed in Damascus, the government says. The opposition says rebels shot it out of the sky. Meanwhile, reports are surfacing that a massacre took place in Daraya.
Syrian forces moved against a town near the capital Thursday, using tanks and artillery to flush out opposition fighters.
Activists report over 30 deaths as a result of the bombardment Wednesday, part of President Assad's campaign to defeat opposition elements across the nation.