Damage and closed shops in Aleppo
Damage and closed shops in AleppoReuters

The head of the UN peacekeeping department confirmed on Thursday that Syria's rebels have heavy weapons, although he said the United Nations had no proof the opposition had used them against government forces.

“We know for a fact that the opposition does have heavy weapons,” UN Under-Secretary-General for Peacekeeping Operations Herve Ladsous was quoted by Reuters as having told reporters. He gave no details on where the arms had come from, but said such weaponry included tanks and armored personnel carriers.

UN officials and diplomats say the rebels have been capturing weapons from Syrian soldiers they have overrun in parts of the country where they have gained an upper hand.

Ladsous said he had no proof the rebels had used heavy weapons against the army, which Syrian President Bashar al-Assad has deployed for 17 months against an increasingly militarized opposition determined to oust him.

The confirmation comes after reports that the rebels turned the gun of a captured tank against government forces, shelling a military airbase north of the city of Aleppo.

It came a day after it was reported that President Barack Obama has signed a secret order authorizing U.S. support for rebels seeking to depose Syrian President Bashar al-Assad and his government.

Sources told Reuters on Wednesday that Obama's order, approved earlier this year and known as an intelligence "finding," broadly permits the CIA and other U.S. agencies to provide support that could help the rebels oust Assad.

The fighting intensified in Syria on Thursday, with Reuters reporting that Syrian forces killed at least 50 people, among them members of three families, during clashes with rebels in the central city of Hama.

Former UN Secretary General Kofi Annan resigned from his post as the UN-Arab League peace envoy for Syria on Thursday, asking that his mandate not be renewed when it expires August 31.

Annan blamed "fingerpointing and name calling" at the UN Security Council for his decision to resign.

A report released jointly on Thursday by the World Food Program and the United Nations Food and Agriculture Organization warned of a food shortage in Syria if the fighting continues.

The Syrian agricultural sector has lost $1.8 billion this year due to the 16-month-old civil war, with the wheat and barley harvest particularly affected. Up to 3 million Syrians are likely to need food, and assistance with crops and livestock in the next 12 months, the report warned.