UN Secretary General Antonio Guterres on Thursday announced a special investigation into the bombing of hospitals and schools by Syria and its Russian backers in the north-western province of Idlib.
The probe follows outrage among leading members of the Security Council at Russia's involvement in air strikes in Idlib since the end of April.
The US, Britain, France and top UN officials have said schools and hospitals have been the targets of bombing and that Russia, a permanent member of the council, has been complicit.
An agreement between Russia and Turkey for a conflict buffer zone in some areas has failed to prevent civilian sites from being hit, leaving the population in danger.
Shortly after the UN announcement, Syrian state news agency Sana reported that the government had agreed to a truce in the Idlib region on condition that the deal between Turkey and Russia was implemented.
A military source said the regime had approved "a ceasefire in the de-escalation zone in Idlib starting from tonight", as long as opposition groups withdrew fighters and heavy weapons from the zone as agreed to in the Russian resort of Sochi last September.
Mr Guterres' spokesman, Stephane Dujarric, said the UN investigation board would "ascertain the facts of these incidents and report to the Secretary General upon the completion of its work”.
“The Secretary General urges all parties concerned to co-operate with the board once it has been established,” he said.
Syrian President Bashar Al Assad is seeking to reclaim Idlib, the last major rebel-held area, to end the war.
His regime and Russia has said that its military action is to root out terrorists and that any hospitals, schools or other civilian buildings hit were not being used as such when targeted.
The province is home to more than three million people, half of whom were displaced from other areas.
On Tuesday, Mark Lowcock, the UN's co-ordinator of humanitarian affairs, said air strikes by Syrian and Russian planes amount to a scorched-earth policy, and he criticised major world powers for being idle on the issue.
“You in this Security Council have ignored all the previous pleas you have heard,” he said in New York.
“You know what is happening and you have done nothing for 90 days as the carnage continues in front of your eyes.
“Are you again going to shrug your shoulders, as Michelle Bachelet said, or are you going to listen to the children of Idlib and do something about it?”
Ms Bachelet, the UN's High Commissioner for Human Rights, last week said at least 450 civilians had been killed since Syria and Russia began their offensive.
Analysis of satellite imagery over the past three months shows that at least 17 villages have been almost completely destroyed, Mr Lowcock said.
Information about the air attacks will be passed on to the Commission of Inquiry for Syria, which is collecting evidence for possible war crimes charges from the more than eight-year war.
Britain's representative at the UN, Karen Pierce, said on Tuesday that a recent letter from the Syrian ambassador to the UN, which admitted at least one hospital on the list of banned sites had been targeted, was confirmation that war crimes were being committed.