The attack came just hours after an airstrike on a nearby area killed six civilians.
The latest attacks show that a nearly three-month fragile truce has collapsed as violence has intensified in and around Idlib province, the last major rebel stronghold in the war-torn country.
The Britain-based Syrian Observatory for Human Rights, an opposition war monitor, said government forces shelled camp Qah, killing 15 and wounding others. The Observatory said the attack caused fires in several tents and added that ambulances rushed to the area and were still evacuating the wounded.
It added that the two surface-to-surface missiles struck an area in the camp close to a maternity hospital. It said the dead included two women and six children.
The Aleppo Media Center, an activist collective, also reported that the government shelled the camp with rockets Wednesday evening, killing 15 and wounding more.
In the rebel-held town of Maaret al-Numan, also in northwestern Syria, an airstrike killed at least six people and wounded others, according to the Observatory and the opposition's Syrian Civil Defense, also known as White Helmets.
Syrian state media reported that insurgents fired shells on the northern city of Aleppo, Syria's largest. It gave no word on casualties.
The latest attacks come after shelling and airstrikes on Idlib province killed and wounded dozens of people in recent days.
Syrian troops launched a four-month offensive earlier this year against the country's last opposition stronghold, which is dominated by al-Qaida-linked militants.
The government offensive forced hundreds of thousands of civilians to flee their homes. A fragile cease-fire halted the advance at the end of August, but in recent weeks it has been repeatedly violated.
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