Syrian rebels stepped up an offensive against government troops Thursday, using a captured tank to bomb a military air base in the commercial capital Aleppo as regime forces in the capital, Damascus, unleased new raids against them.

President Bashar al-Assad's troops retaliated in Aleppo by pounding the strategic Salaheddine district with tank and artillery fire as rebels tried to consolidate their hold on areas they have seized.

The Britain-based Syrian Observatory for Human Rights says government forces shelled a neighborhood in the city, killing seven civilians.

Fighting in Syria's most populous city, Aleppo, continues to rage on after two weeks of clashes,

Activists also say security forces launched a raid Wednesday in the Damascus area that killed dozens of people. Syrian state media said the operation targeted “terrorists,” a reference to the rebels.

Meanwhile, U.S. sources told western media that President Barack Obama signed an order earlier this year allowing the Central Intelligence Agency and other U.S. agencies to provide support to the rebels.

The National Security Council declined to comment to VOA about the report.

The United Nations said Thursday nearly 3 million people in Syria are in need of food assistance, and further warned that half of those need “urgent and immediate” aid in the next three to six months.

The U.N. Food and Agriculture Organization issued a statement along with the World Food Program saying the 17-month crisis in Syria has cost the country's agricultural sector $1.8 billion. But it said the humanitarian impact is far more important.

The findings are based on a joint assessment by the U.N. and the Syrian government.