Russia has halted air strikes in Syria in accordance with a ceasefire brokered by the country and the US.

Russia entered the Syrian conflict on behalf of ally President Bashar al-Assad in September 2015, and its air power has played a significant role in the recent major gains by government forces.

"Russia's air force fully halted bombing in the green zone - that is in those areas and those armed groups which had sent us ceasefire requests," Lieutenant-General Sergei Rudskoi, a senior representative of the General Staff, said.

A lull in fighting was reported throughout most of Syria on Saturday, hours after the US-Russia brokered "cessation of hostilities" agreement took effect.

READ MORE: Inside Story - will a ceasefire hold in Syria?

The UN Security Council unanimously passed a vote late on Friday to support the pause in fighting in Syria, and demanded that all parties to the agreement fulfill their commitments to end hostilities.

The ceasefire began at midnight Damascus time on Saturday (22:00 GMT Friday).

Al Jazeera's Omar al-Saleh, reporting from Turkey's Gaziantep on the Syria border, said: "The situation is calm - the truce is largely holding - for the first time in many years.]

"The airbase in Latakia, which the Russians use for their air strikes, is very calm as well."

Rudskoi said while Russia would continue air strikes against the Islamic State of Iraq and the Levant (ISIL) group and al-Qaeda's branch in Syria, al-Nusra Front, it was keeping its aircraft on the ground for now "to avoid any possible mistakes".

He said Russia had given the US maps showing the location of opposition groups pledging to abide by the ceasefire, as well as ISIL and al-Nusra Front units.

He said 74 opposition units - including more than 6,100 fighters - had agreed to adhere to the truce.

While there were no reports of air strikes or heavy artillery fire, violence was reported on Saturday.

In desperate need

Al Jazeera's Mohammed Jamjoom, reporting from Beirut in neighbouring Lebanon, said there had been no reported air strikes in areas included in the ceasefire, explaining that several communities across Syria were still in desperate need of humanitarian aid.

The High Negotiations Committee (HNC) "has complained even as late as today that there are areas inside Syria ... that need to get aid", including medical supplies, food and water, he said, referring to Syria's main opposition bloc.

"Activists there on the ground, especially opposition activists, say that aid is needed," he said, adding that they were "urging the UN and other aid organisations".

A Syrian rebel group in the country's northwest said it came under attack from government ground forces at 4am local time (02:00 GMT) in what it called a breach of the cessation of hostilities plan.

Three fighters from the rebel First Coastal Division were killed while repelling the attack in the Jabal Turkman area near the Turkish border in Latakia province, Fadi Ahmad, the group's spokesman, told Reuters news agency.

Barrel bomb reports

There were also reports of Syrian helicopters dropping barrel bombs. The Syrian military could not immediately be reached for comment.

Elsewhere on Saturday, a suicide car bomb exploded on the edge of Salamiyeh, a government-held central town, killing two people and wounding four others, the state news agency said.

COMPASS - The Invisible railroad for Syrian refugees

Countries backing the Syrian peace process meet on Saturday in Geneva to assess the situation.

The Syrian government has previously said it would abide by the truce, but would have the right to retaliate for any attacks.

The deal marks the biggest diplomatic push yet to end Syria's five-year war, which has killed more than 260,000 people and displaced millions from their homes.