The US-Russian truce deal on “cessation of hostilities” in Syria came into effect at midnight Damascus time. The ceasefire does not apply to Islamic State (IS, formerly ISIS/ISIL), Al-Nusra, or “other terrorist organizations” designated by the UN.

Earlier on Friday, the United Nations Security Council unanimously adopted a resolution urging all parties involved in Syrian civil war to adhere to the terms of the US-Russian deal.

The US-Russia brokered ceasefire was first announced on February 22 by Russian President Vladimir Putin and US President Barack Obama.

Under the “Terms for a Cessation of Hostilities in Syria,” the participants of the agreement are obligated to “cease attacks with any weapons, including rockets, mortars, and anti-tank guided missiles” and “refrain from acquiring or seeking to acquire territory from other parties to the ceasefire.” They must also allow “unhindered and sustained” access to humanitarian assistance missions and employ only “proportional force” in self-defense against those not party to the agreement.

The truce will be monitored by a task force co-chaired by Moscow and Washington. Russia and the US are to “work together to exchange pertinent information,” such as up-to-date maps indicating which sides have agreed to the ceasefire, and where they are located.

Earlier on Friday, the Syrian opposition taking part in the Geneva talks announced that they would respect the truce.

“The High Negotiations Committee (HNC) confirms the agreement of the Free Syrian Army factions and the armed opposition to a temporary truce from midnight Saturday,” an HNC statement said, as quoted by Reuters.

Damascus has supported the ceasefire, but says it will not tolerate terrorists exploiting it in order to restore their positions or receive support from abroad.

The UN stated that in the case that the truce is broken by an attack, a response employing force must not only be proportional, but also used only as a last resort.

UN Syria envoy Staffan de Mistura said there had been several incidents reported in Damascus and Deraa in the first few minutes of the ceasefire, but that things quickly de-escalated.

Mistura also said that his office was looking into another breach, but didn’t provide any details.

“Let’s pray that this works, because frankly this is the best opportunity we can imagine the Syrian people has had for the last five years in order to see something better, and hopefully something related to peace. Facts will tell,” Mistura said.

A total of 97 armed groups operating in Syria have agreed to the ceasefire, Mistura added at the UNSC.

Syria’s Permanent Representative to the UN, Bashar Jaafari, said that the Syrian Army has the right to respond to “any violations” of the ceasefire.

He also described the US-Russia agreement as “an important step” towards achieving a political resolution in Syria, while stressing the importance of cutting off support to the terrorists groups there. The comments were made to the UNSC on Friday.

Media reports suggest that it has been calm in Damascus since the ceasefire began. In particular, AP has reported that its reporters on the scene have not heard any explosions in the capital since three minutes before the truce came into effect.

The news agency also cited an opposition member as saying that the Damascus suburb of Ghouta is quiet. “Eastern Ghouta is quiet for the first time in years,” Mazen al-Shami said.

Fighting has also reportedly stopped in the southern city of Daraa. Another opposition fighter, Ahmad al-Masalmeh, told AP, “In the first half an hour of the ceasefire, the situation is relatively calm but tense.”

There have also been no reports of airstrikes since midnight.

It will be important to keep the fight against terrorists groups going in Syria, RT’s Lizzie Phelan reported from Aleppo, citing a heavy extremist presence in certain areas of the city, which is located in the northern part of the country.

The Syrian army said that Jabhat al-Nusra, Al-Qaeda’s branch in Syria, and Islamic State (IS, formerly ISIS/ISIL) maintain a strong presence in parts of the city currently held by opposition forces.

“We can see their flags everywhere,” a Syrian soldier told RT.

Phelan also added that the Syrian Army is determined to fight terrorist groups that are not part of the truce.

“In some areas there may be a ceasefire, but in most of Aleppo and surrounding countryside, it’s Al-Nusra and ISIS, and we won’t stop fighting until we get rid of them,” a Syrian officer said.

In general, the US has taken a rather skeptical stance towards the truce’s prospects for success. Nevertheless, Obama has said his administration will do everything in its power to make it work.

In a televised statement after the ceasefire plan was announced, Putin said that “this is a real chance to stop the bloodshed in Syria,” as well as to deliver humanitarian aid.

In the meantime, the US has been discussing “Plan B” options, in case the truce agreement in Syria fails, Secretary of State John Kerry told a Senate committee on Wednesday, although he failed to specify what those Plan B options could be.

On the other hand, Russia says that it hasn’t discussed any “Plan B” options for Syria and finds it surprising that America has. “We’re perplexed by our Western partners, the US included, mentioning the existence of some kind of ‘Plan B,’ Nothing is known on that one, we are considering no alternative plans,” Deputy Foreign Minister Mikhail Bogdanov said on Thursday.