France's foreign minister on Tuesday accused the Syrian government and Russia of probably carrying out war crimes in their offensive in northwestern Syria, adding that Paris would document them.

"The offensive by the Syrian government is made possible by Russian air support and marked by systematic violations of human rights," Jean-Yves Le Drian told lawmakers.

"It's for this reason that I say... that we consider today that these violations are possibly liable to being considered war crimes and we will document them."

Open gallery view French Foreign Minister Jean-Yves Le Drian leaves the Elysee Palace following the weekly cabinet meeting in Paris, France, October 21, 2019. Credit: Benoit Tessier/ REUTERS

Earlier on Tuesday, the Kremlin rejected allegations by the United Nations that Russia may have committed war crimes in Syria last year, saying the UN investigators were in no position to know what is happening on the ground.

"We strongly reject these accusations," Kremlin spokesman Dmitry Peskov said. "It's obvious that one commission can not have reliable information of what is happening on the ground."

A report released on Monday by a UN commission found that Russia - the Syrian government's main ally against rebels and militants - conducted air strikes on a popular market and a camp for displaced people that killed dozens of civilians in July and August.

"In both incidents, the Russian Air Force did not direct the attacks at a specific military objective, amounting to the war crime of launching indiscriminate attacks in civilian areas," the report said.

Peskov said the report failed to take into account attacks by militant groups which meant that at the very least the judgements of the commission were one-sided.

"We absolutely do not agree with these statements," he said.

The UN report blamed Russia for an air strike in the city of Maarat al-Numan on July 22 when at least 43 civilians were killed. Two residential buildings and 25 shops were destroyed after at least two Russian planes left Hmeimim air base and circled the area, it said.

"We have reasonable grounds to believe that these were Russian planes with Russian pilots," said UN commission panel member Hanny Megally.

Open gallery view A Syrian army soldier carries food as he walks through Maarat al-Numan, Syria January 30, 2020. Credit: YAMAM AL SHAAR/ REUTERS

Monday's report covered the period from July 2019 to mid-January 2020.

Since December, around one million people have been displaced from Syria's northwestern Idlib region as the fighting has escalated, in what the UN says may be the worst humanitarian crisis in nine years of war.

Russia's Defence Ministry said statements by Turkey and other Western countries regarding the flow of refugees and a humanitarian crisis in the region were groundless, the Interfax news agency reported.