WASHINGTON — (CNN) War-ravaged Syria has entered its first day of a nationwide ceasefire brokered by Russia and Turkey.

Syria’s military said it halted operations at midnight, except against ISIS and other terror groups, the state-run Syrian Arab News Agency (SANA) reported.

A UK-based activist group said there were signs of pockets of violence early Friday, but large areas of the country were calm.

“Most areas in Syria are quiet since the start of the ceasefire, but violent clashes were reported less than two hours after it took effect in the Hama suburbs between regime forces and rebel fighters in Tal Beejo in northern Aleppo, causing regime forces to withdraw,” said Rami Abdulrahman of the UK-based Syrian Observatory for Human Rights.

Neither SANA nor Russian state media has reported episodes of violence Friday morning.

On Thursday, Russian President Vladimir Putin announced the agreement that the Syrian government and opposition rebels would cease fighting in the country’s long-running civil war. Putin described the agreement as “very fragile” and said it demanded “special attention and patience.”

The brutal civil war has raged on for nearly six years and killed an estimated 400,000 people.

Putin said the two sides agreed to enter peace talks to end the conflict, according to the Russian state-run TASS news agency. Three documents had been signed, Putin said: the ceasefire agreement, a package of measures to oversee the ceasefire and a declaration of readiness to enter into peace talks.

Those peace talks are to be held in Astana, Kazakhstan, in what Putin and Syrian President Bashar al-Assad had described as “an important step for a final solution of the crisis,” according to a statement by the Kremlin.

Putin and Assad had discussed the agreement by phone Thursday, with the Syrian president saying he would comply with the ceasefire, according to a Kremlin statement.

Turkey and Russia are guarantors to the agreement.

But groups considered as terror organizations by the UN Security Council, such as ISIS, are excluded from the agreement, the Turkish Ministry of Foreign Affairs said.

The latest effort comes after previous ceasefire attempts by the international community crumbled.

It also follows several ceasefire agreements brokered by Turkey and Russia in the city of Aleppo this month. Most were broken, but one held long enough to allow the evacuations of tens of thousands of rebels and civilians from eastern Aleppo.

Eastern Aleppo had been under rebel control for four years and had been choked off by the Syrian regime, leading to shortages of food and supplies for civilians.

The Syrian regime then gained full control of Aleppo, a major turning point that has limited the opposition’s military and political options.

“We’ve had these rebel reverses, the loss of Aleppo — a victory by the Syrian regime,” said CNN military analyst Lt. Col. Rick Francona.

“So I think that the rebels are looking at this as maybe their last chance, and they may actually want this ceasefire to work. … But their hand is really weak right now.”

A successful nationwide ceasefire hinges on many fighting factions laying down arms. Groups from Iraq, Iran and Lebanon are also fighting alongside the forces of Assad.

The legal adviser for the Turkish-backed rebel Free Syrian Army, Osama Abu Zeid, called the agreement “a complete truce with no exceptions or preconditions” that included “all areas and military factions in Syrian opposition territory.”

“The main goal is improving the living conditions for Syrian citizens,” he said.

“Our message to the Syrian population (is) that our fingers will remain on the trigger, and we will present all sacrifices and we will take every path that will alleviate the suffering of the Syrian people.”

Not all opposition groups have signed the latest ceasefire, though. The Syrian rebel group Ahrar al-Sham is one of them.

“Ahrar al-Sham has a number of reservations over the proposed agreement and the negotiations,” spokesman Ahmad Qura Ali said on Twitter. “We will make clear our reservations in due course.”

Turkey and Russia appear to be sidelining the United States and driving what had been a UN-led political process.

Throughout the Syrian war, the UN Security Council has been widely criticized for failing to find a solution. Russia has played a role in that, as it used its veto power to reject several resolutions on the conflict.

A spokesperson for UN Special Envoy to Syria Staffan de Mistura welcomed the ceasefire in a statement.

US State Department spokesman Mark Toner acknowledged that Washington was not part of the negotiations but said the agreement was “a positive development.”

The US has led an international coalition to fight ISIS in Syria and has vehemently opposed any attempt to keep Assad in power.

Although Russia and Turkey brokered the agreement, the two countries have differed in their stance on Assad, whose family has ruled Syria for four decades.

Turkish President Recep Tayyip Erdogan said last month that Turkish forces entered Syria to help end Assad’s rule.

Meanwhile, Russia is Assad’s most powerful ally and has propped up his regime since September 2015 with airstrikes.

Putin said Russia would begin scaling back its military presence in Syria, though it would continue to support the “legitimate Syrian government in its struggle with terrorism.”

The Syrian regime has frequently referred to opposition fighters as “terrorists,” long before ISIS gained a foothold in the country.