The UN's Syria envoy said Thursday that visible progress was being made on the country's landmark ceasefire, after a sharp drop was reported in the number of civilians dying every day.

France and Britain said further efforts were needed, calling on Russia to halt attacks on moderate rebel groups in Syria as the country suffered an hours-long nationwide blackout, evidence of the damage nearly five years of war has inflicted.

World powers have thrown their weight behind the ceasefire agreement as a way to bring an end to the complex war, starting with renewed peace talks in Geneva set for March 9.

Peace envoy Staffan de Mistura on Thursday said the truce, now in its sixth day, had made "visible" progress.

"The level of violence in the country is being greatly reduced. Ask the Syrian people," De Mistura told reporters in Geneva, adding that the situation remained "fragile".

He spoke before entering a meeting of the UN-backed international task force co-chaired by Moscow and Washington that is overseeing the truce.

"In general, the cessation has been holding," he said, while acknowledging that "there are still a number of places where fighting has continued," including in parts of Damascus and Homs.

- 'Huge drop' in deaths -

One of the clearest signs that the truce is largely holding has been a drastically lower civilian death toll.

In the five days since the ceasefire took effect, a total of 73 civilians were killed across the country, according to the Syrian Observatory for Human Rights.

The monitoring group said 49 of the civilians were killed in areas controlled by the Islamic State jihadist group, which along with Al-Qaeda's local affiliate are not included in the truce.

Observatory head Abdel Rahman said the five-day toll represented a "huge drop," comparing it with the 63 civilians killed on Friday alone, before the cessation of hostilities.

On Thursday, activists and AFP correspondents reported one of the quietest days so far.

In Aleppo, vegetable markets and parks were teeming with grinning families enjoying the calm, an AFP correspondent said.

And in Daraya, a rebel-held town near Damascus, activist Shadi Matar said children could finally enjoy a full day of school.

"Before the truce, students would start at 6:00 am before the barrel bombs start, and the school day would only last two hours," he said.

But in a reminder of the toll the war has taken on infrastructure, Syria was hit by an hours-long nationwide power cut on Thursday.

Syrian state television said power was slowly returning to parts of the country after the widespread blackout began at 1100 GMT, without specifying the cause.

- Calls to Russia -

Syria's government and the opposition -- and their respective backers -- have traded accusations over ceasefire breaches.

The head of the main opposition grouping, the High Negotiations Committee, said on Thursday the truce would be "on the verge of collapse" if world powers did not do more to stop violations.

Riad Hijab said the regime and its allies had committed more than 100 breaches over the past five days.

Russia's defence ministry said however it had recorded 44 breaches of the truce from the rebel side since Wednesday.

A statement said Russia had documented 14 instances of shelling of regime-held residential areas, adding four tonnes of Russian humanitarian aid was delivered to the central Hama province during a 24-hour period.

French President Francois Hollande and British Prime Minister David Cameron called on Russia and the Syrian regime to "immediately stop attacks on the moderate opposition".

Hollande, Cameron, and German Chancellor Angela Merkel will discuss the truce on Friday in a conference call with Russian President Vladimir Putin, Downing Street said.

"Tomorrow is an opportunity for the leaders of the UK, France and Germany to come together... and make very clear to President Putin that we need this ceasefire to hold, to be a lasting one and to open the way for a real political transition," Cameron's spokeswoman said.

On Wednesday, Cameron said the ceasefire was "an important step forward, imperfect as it is", as it opened the way to the prospect of political negotiations.

bur-mjg/pg/dv

ASK