The United Nations is calling on all parties in Syria to de-escalate the conflict in face of reports that at least 19 people have been killed by recent shelling and airstrikes in the country's northwest, a UN spokesperson said on Wednesday.

"The UN calls on all parties to the conflict to de-escalate the situation in the northwest," said Stephane Dujarric, spokesperson for UN Secretary-General Antonio Guterres.

The UN also reminds all parties of their obligations to protect civilians under international humanitarian law, including following the principles of distinction, proportionality and precautions in the conduct of military activities.

In the past few days, dozens of communities have been impacted by airstrikes, artillery shelling, resulting in deaths and displacement, said the spokesperson at a regular briefing.

He said that reports from humanitarian colleagues of the UN indicated that at least 10 people were killed following an airstrike on a local market in a town in Idlib Governorate and at least nine people were killed following artillery shelling in Tal Rifaat in north rural Aleppo Governorate.

Dujarric said those colleagues remain deeply concerned for the safety and protection of more than four million civilians in northwest Syria following an upsurge in violence and hostilities in the area. More than half of the population is internally displaced.

The UN Human Rights Office has documented that 1,000 people were killed between April and August, and an estimated 400,000 people displaced, the spokesperson said.