Russian servicemen in sand-coloured fatigues sit by phones and computer screens at a base in northwestern Syria, monitoring a ceasefire often on the brink of collapse.

In coordination with a US centre in the Jordanian capital, soldiers at Russia's Hmeimim airbase record breaches of the truce -- brokered by Moscow and Washington -- from barracks converted into a makeshift call centre.

"This is our direct line to Amman," said the head of the ceasefire monitoring centre, Lieutenant General Sergei Kuralenko, pointing to a telephone.

"And these two phones are for calls from any resident of Syria and from citizens of the world."

Russia began a major bombing campaign in support of its longtime ally President Bashar al-Assad in September, enabling regime forces to seize back territory.

A ceasefire introduced on February 27 between the government and non-jihadist rebels largely held for several weeks before starting to fall apart as fighting surged in Syria's divided second city Aleppo.

While Kuralenko showed off satellite images attesting to Moscow's monitoring work to journalists on Wednesday during a press tour organised by the Russian defence ministry, deadly violence raged in Aleppo.

On Thursday a new 48-hour ceasefire took hold in the northern city as Assad's regime and rebel forces gave in to mounting diplomatic pressure.

Aleppo had been left out of the so-called "regime of silence" -- reportedly at Moscow's request -- declared last week in a bid to salvage the February 27 ceasefire.

World powers have since stepped up diplomatic efforts to end violence in the city that has claimed the lives of 280 civilians since April 22.

Kuralenko accused rebel groups of responsiblity for most of the truce violations.

Russian defence ministry spokesman Igor Konashenkov blamed attacks by Syrian Al-Qaeda affiliate Al-Nusra Front for preventing Aleppo's initial inclusion in the fighting freeze.

"As of today the regime of silence (in Aleppo) has been prevented by the terrorist group Al-Nusra," Konashenkov said on Wednesday, accusing the extremist movement of perpetrating rocket attacks on residential areas of Aleppo.

Konashenkov, however, underlined that the freeze in fighting along two major fronts in Syria's northwest and the Damascus region was overall being respected.

- Hopes for villagers' return -

In the village of Kawkab, northeast of Damascus, elderly men in chequered headdresses, accompanied by Russian colonels, participated in the signing of a local agreement allowing residents to return after the area was recaptured from Al-Nusra.

Locals danced alongside Kalashnikov-wielding Syrian soldiers while children in dusty clothes brandished Syrian flags and portraits of Assad. Around the corner, Russian servicemen unloaded humanitarian aid trucks.

"Some 10,000 people used to live here," a local leader, Ahmed Mubarak, said through a translator. "I don't know how many there are now, but I am sure that in four days they will be back."

Located near a frontline, Kawkab was recaptured by government forces about a year ago, locals said, but residents had not felt it was safe to return until recently.

"Russia has played a significant role in the peace process," Mubarak said, echoing statements by Russian defence officials. "Of all countries it has provided the most aid."

Since President Vladimir Putin ordered a partial withdrawal of Russian forces from Syria in mid-March, Moscow has presented itself as a key peacemaker on the ground.

Konashenkov said that more than 90 towns and villages and 52 rebel groups had signed local truces with government forces that have Moscow's backing.

He said that these local agreements had seen around 7,000 fighters lay down their arms.

"That's a lot," he said.

Russia has been a key player in UN-mediated talks between the regime and opposition forces but has dismissed calls for Assad to step down.

The Kremlin has insisted the West should focus its efforts on ending the five-year conflict that has killed more than 270,000 people before it can tackle extremist organisations such as the Islamic State group.