BEIRUT (Reuters) - Syrian government forces clashed with rebels in Hama province on Friday in some of the heaviest fighting in the northwest for a year, the Syrian Observatory for Human Rights said.

The army and allied forces attacked insurgents near the village of Halfaya overnight, seizing some positions, the UK-based war monitoring group said.

State news agency SANA said soldiers killed insurgents in an ambush in Hama “in response to their attacks on a military position with heavy machineguns”.

The Observatory said it was unclear if pro-government forces were killed. At least 22 members of the Jaish al-Izza faction died and dozens more were wounded, the highest casualty toll of fighters in the northwest in many months, it said.

Intermittent exchanges of fire have broken out in northwest Syria since a deal in September between Russia, a key Damascus ally, and Turkey, which has backed the opposition.

The agreement to set up a 15-20 km (9-13 mile) deep demilitarized zone staved off an army offensive against the Idlib region that is under insurgent control, including nearby parts of Hama and Aleppo provinces.

The Observatory said government forces shelled parts of Jarjanaz, Khan Sheikhoun and other villages on Friday.

The United Nations says nearly 3 million people live in the northwest region and has warned that a battle to restore state rule there could spark great suffering.

An array of insurgents control Idlib, the dominant force being Tahrir al-Sham, an Islamist alliance led by fighters formerly linked to al Qaeda.