The defence ministry said violations were committed by moderate rebels as well as "terrorist organisations".

"Over the past 24 hours nine instances of violations of cessation of hostilities have been uncovered" the ministry said citing its coordination centre at the Hmeimim airbase in Syria.

"On the whole the ceasefire regime in Syria is being implemented" it said of the deal brokered by Moscow and Washington which took effect from 2200 GMT Friday.

"At the same time there are a number of violations by groups of 'moderate' opposition and units of international terrorist organisations."

The ministry highlighted an attack on the town of Tal Abyad on the border with Turkey.

A group of up to 100 fighters who crossed the border from Turkey mounted an attack on the northern part of Tal Abyad it said adding they were acting in unison with other fighters.

- 'Fire from Turkish territory' -

"The activities of the armed groups were supported by artillery fire from Turkish territory" the chief of the coordination centre Lieutenant General Sergei Kuralenko said in televised remarks.

"Kurdish rebel units had pushed the fighters out of the city by morning of February 28."

Moscow said it had demanded an explanation from the United States which leads an anti-IS coalition that includes Turkey.

Turkey has said it is not bound by the ceasefire deal if its national security was threatened.

The Tal Abyad attack was "confirmed through several channels including representatives of the Syrian Democratic Forces" Kuralenko was quoted as saying by Russian reporters referring to a US-backed Kurdish-Arab alliance.

According to the Syrian Observatory for Human Rights the Kurdish forces and their Arab allies successfully pushed back a fierce IS offensive by Saturday night with backing from the US-led coalition.

In Latakia Al-Nusra Front jihadists acting from territory controlled by moderate rebels shelled a unit of Desert Falcons the Russian ministry said apparently referring to an Iranian-backed regime force.

"As a result of the shelling there are a lot of dead and wounded among rebels and locals."

Russia also said Damascus was shelled six times Saturday adding that the attack came from territory controlled by moderate rebels including Eastern Ghouta east of the capital.

"All in all 20 mine and missile explosions have been recorded" Moscow said adding two civilians were killed and eight wounded.

"At the request of the Russian centre for reconciliation Syrian government troops did not open return fire" the ministry said.

Moscow said its coordination centre had also received a US list of 69 armed groups who had confirmed their willingness to observe the ceasefire.