CAIRO - At least 18 civilians were killed on Sunday in airstrikes believed to have been carried out by Russian warplanes in northern Syria, a monitoring group said.

The airstrikes targeted the rebel-held town of Ariha in the northwestern province of Idlib, the Syrian Observatory for Human Rights said.

The Britain-based group said the attacks also injured dozens seriously.

Local activists put the number of the dead at 40, claiming that the airstrikes hit a market.

There was no comment from Damascus or Moscow.

Islamist rebels, including al-Qaida-linked Nusra Front, have controlled Ariha since May.

Russia, an ally of Syrian President Bashar Assad, says its airstrikes, which began Sept. 30, are aimed at Islamic State and other extremist groups.

The human rights group also said Sunday that Islamic State has executed at least 53 people, including 35 civilians, in a month in Syria.

The victims were convicted on charges including apostasy, spying, homosexuality, adultery and sorcery.

The executions were carried out from Oct. 29 to Sunday in Islamic State-held areas in Syria including Raqqa, the de facto capital of the al-Qaeda splinter group.

Also Sunday, Prime Minister Ahmet Davutoglu criticized Russian economic sanctions on Turkey after the downing of a Russian fighter jet over the Syrian border last week, saying his priority was to defuse the tension and prevent similar incidents.

Russian President Vladimir Putin on Saturday announced measures against Turkey including the suspension of visa-free travel, halting tours to Turkey and a ban on the hiring of Turkish nationals. In Turkey, Deputy Prime Minister Mehmet Simsek chaired a meeting with other members of the nation's economic administration to discuss the potential impact, according to a government official, who asked not to be named in line with official policy.

Bloomberg's Constantine Courcoulas and Benjamin Harvey contributed to this article.