Syrian government warplanes struck a market and an industrial area Wednesday in the last territory in the hands of rebel groups in the country's northwest, killing at least 15 people, opposition activists said.

A new cessation of hostilities agreement between Russia and Turkey, who support the opposite sides in the conflict, went into effect last week. But violence has continued.

Yahya Abu al-Yaman, a volunteer with first responders the Syrian Civil Defense, said 15 people were killed and 65 were wounded in the strike. Most were in critical condition after warplanes struck a vegetable market and industrial area in Idlib city Wednesday afternoon. The two areas are a few hundreds meters (yards) apart.

The Syrian Civil Defense, also known as the White Helmets, said one of its volunteers was killed in the strike.

The Britain-based Syrian Observatory for Human Rights said the two areas were crowded with people when the warplanes struck. It also put the death toll at 15.

Open gallery view A destroyed building following a regime air strike on Ariha town in Syria's last major opposition bastion of Idlib, January 15, 2020. Credit: AFP

The Observatory said airstrikes were also reported in other parts of Idlib province, recording at least 42 Russian raids and 33 by government warplanes. The Observatory has a network of activists on the ground and has been monitoring the war in Syria since it began in 2011.

The government also launched several barrel bombs from helicopters in rural Idlib, according to the Observatory. The bombs are rudimentary and inaccurate projectiles that cause massive destruction.

Russia is a main backer of Syrian President Bashar Assad, while Turkey is a strong supporter of some of the insurgents fighting against him. Moscow blamed the insurgents for violating the truce Saturday.

Idlib is controlled by armed rebel groups, including Turkey-backed opposition groups and Al Qaida-linked militants who are the strongest there. It is also home to 3 million civilians. The United Nations said at least 300,000 have been displaced by the violence in the month between December 1 and January 1.

The international body, which is responsible for delivering most of the aid to Idlib, has warned of the growing risk of a humanitarian catastrophe as people flee the fighting toward the Turkish border.

Cease-fires have failed to quell the violence. A government offensive that began last month appears aimed at reopening the highway linking the capital Damascus with the northern city of Aleppo, Syria's largest. The highway has been closed in Idlib since 2012, when insurgents captured several towns along the route.