Russia and the United States have discussed ways of supporting the ceasefire in Syria through co-operation between their militaries. Russian Foreign Ministry said in a statement that in a telephonic conversation, Russian Foreign Minister Sergei Lavrov and US Secretary of State John Kerry hailed the ceasefire, and recognised the importance of working together as co-chairs of the 17-nation International Syria Support Group.

The Russian military, earlier, said its warplanes had suspended all sorties over Syria to avoid any bombing mistakes and the US and Russia militaries also exchanged maps of Syria.

It is the first major truce in a five-year war that has claimed 270,000 lives and displaced more than half of Syria’s population.

UN Secretary-General Ban Ki-moon’s spokesman Stephane Dujarric has said, the first day of the ceasefire in Syria led to reduction in violence in the conflict-torn country.

President Barack Obama has however warned that violence between the country’s warring parties will not end immediately.

“Even under the best of circumstances, the violence will not end right away,” the American president said in his weekly address. “But everyone knows what needs to happen.”

Brokered by the U.S. and Russia earlier this week, the pause in fighting is expected to allow humanitarian aid to reach Syrian civilians in dire need of basic supplies.

Al-Qaeda’s Syria affiliate, the Nusra Front, and Daesh, are not party to the agreement, and Obama has pledged to continue to strike Daesh without pause.

“We’ll remain relentless,” he said. “We will destroy this barbaric terrorist organization and continue to stand with those around the world who seek a better, safer future.”

Less than an hour before the deal was set to take effect, the UN Security Council unanimously adopted a resolution endorsing the cessation of hostilities.

The resolution demanded “all parties to whom the cessation of hostilities applies … fulfill their commitments” and urged major countries to use their influence with the warring parties “to support efforts to create conditions for a durable and lasting cease-fire”.

Critically important is Russia and the Syrian government’s adherence to the deal, Obama said.

“Much will depend on whether the Syrian regime, Russia and their allies live up to their commitments. The coming hours and days will be critical, and the world is watching,” he said.