Air strikes and clashes in Syria's second city Aleppo killed at least 12 people Wednesday, state media and emergency workers said, part of a surge in violence straining a two-month-old ceasefire.

State news agency SANA said that seven people were killed and 35 wounded by rocket and gunfire in several neighbourhoods that it blamed on Al-Qaeda affiliate Al-Nusra Front and its allies.

In rebel-held eastern Aleppo, five civilians were killed in two neighbourhoods, according to the civil defence, known as White Helmets.

An AFP correspondent said that regime aircraft targeted one area with barrel bombs and another with missiles.

Following a lull in fighting after the ceasefire took effect on February 27, violence has intensified in recent days, with more than 100 civilians reported dead in air strikes, shelling and rocket fire since Friday.

Once Syria's commercial hub, Aleppo has been divided between rebel control in the east and government forces in the west since 2012.

The fighting has put the ceasefire in jeopardy and overshadowed a new round of UN-brokered peace talks in Geneva that were entering a recess on Wednesday.

More than 270,000 people have been killed in Syria and millions been forced from their homes since the conflict erupted in 2011.

Russia applauds cooperation with US over Syria
Moscow (AFP) April 27, 2016 - Russia's defence ministry on Wednesday applauded Moscow and Washington's cooperation over Syria as a truce brokered by the two nations was tested by a recent spike in violence.

"Overall, we positively assess the cooperation with the United States in Syria," defence minister Sergei Shoigu said at an international security conference in Moscow.

"Our bilateral agreements on the prevention of incidents in the airspace are working, the military structures responsible for the reconciling the parties are interacting."

Shoigu said Moscow and Washington "must cooperate more closely" in the fight against international terrorism.

"We are ready for this," he said. "The ball is in Washington's court."

In a phone call last week, Russian President Vladimir Putin and his US counterpart Barack Obama agreed to work to strengthen the ceasefire which took effect on February 27.

After taking hold, the landmark partial ceasefire dramatically reduced violence across much of Syria, raising hopes that a lasting deal to end the bloodshed could be struck at peace talks in Geneva.

But a series of recent deadly air strikes and shellings have undermined the frail truce.

On Tuesday, 25 civilians were reportedly killed in air strikes and shelling on Syria's second city Aleppo and a town to its west, in a new test for the troubled ceasefire.

Earlier this month, Syria's main opposition group, the High Negotiations Committee, halted its formal participation in the Geneva talks over surging violence on the ground.

The Kremlin said both Putin and Obama had stressed the "significance" of the Geneva talks and the two also agreed that their security services and defence ministries would ramp up cooperation over Syria.