A rocket attack on a crowded market in a town held by Turkey-backed opposition fighters in northern Syria Friday killed at least nine people and wounded dozens, an opposition war monitor and a paramedic group reported.

The attack on the town of al-Bab came days after a Turkish airstrike killed at least 11 Syrian troops and U.S.-backed Kurdish fighters. The Syrian Observatory for Human Rights, an opposition war monitor, blamed Syrian government forces for the shelling, saying it was in retaliation for the Turkish airstrike.

The Observatory said the attack killed at least 10 and wounded more than 30.

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The opposition’s Syrian Civil Defense, also known as White Helmets, had a lower death toll, saying nine people, including children, were killed and 28 were wounded. The paramedic group said its members evacuated some of the wounded and the dead bodies.

Discrepancies in casualty figures immediately after attacks are not uncommon in Syria.

Turkey has launched three major cross-border operations into Syria since 2016 and controls some territories in the north.

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Although the fighting has waned over the past few years, shelling and airstrikes are not uncommon in northern Syria that is home to the last major rebel stronghold in the country.

Syria’s conflict that began in March 2011, has killed hundreds of thousands and displaced half the country’s pre-war population of 23 million.

President Bashar Assad’s forces have regained control of most parts of Syria over the past few years, with the help of their allies, Russia and Iran.