Syrian government forces mounted new ground attacks against rebel-controlled neighborhoods in Syria's commercial hub of Aleppo, the state media said on Monday, but failed to dislodge the opposition from their strongholds, according to activists.

The Syrian army has massed its forces around Aleppo, where rebels hold several neighborhoods after a 10-day offensive, and has been pounding it with tanks and helicopter gunships. There have also been periodic incursions of government tanks but the rebels have held on to their gains.

This use of heavy weapons, particularly helicopters, is just another nail in President Bashar al-Assad's coffin, US Defense Secretary Leon Panetta said late on Sunday during a stopover in Tunisia as he kicked off a Middle East tour expected to focus heavily on the unfolding crisis in Syria.