Turkish anti-terrorist police have detained 38 foreigners including women and children who were reportedly seeking to join the Islamic State group in Syria, media reports said Monday.

Turkey has gone on the offensive against IS suspects ahead of the G20 summit in the Mediterranean resort of Antalya and after a spate of bloody attacks blamed on the jihadists.

Apparent Russian air strikes killed at least 11 civilians on Sunday in two towns in Syria's northwestern Idlib province, a monitoring group said.

Nine people, including a child, were killed in strikes on areas in the town of Maaret al-Numan, the Syrian Observatory for Human Rights said.

The head of Britain's armed forces on Sunday said the country was "letting down" allies by not participating in air strikes against Islamic State group jihadists in Syria.

Britain is part of a coalition hitting IS targets in Iraq, but its parliament has yet to be convinced of the need to join air strikes in neighboring Syria and an influential committee of MPs recently advised against action.

The Islamic State group on Saturday released 37 Syrian Christians, most of them women, who were among more than 200 people kidnapped more than eight months ago, an NGO said.

The Assyrian Monitor for Human Rights said the group of freed Assyrian Christians included 27 women and 10 men, most of them elderly.

At least 19 civilians and several Islamic State group fighters were killed Thursday in air raids against jihadist positions in the Syrian town of Bukamal, near the border with Iraq, a monitor said. 

"At least 19 civilians, including a woman and two children, as well as jihadists were killed by warplanes" in the town, the Syrian Observatory for Human Rights said, adding it was unclear which country carried out the bombing raids.

Jihadists on Thursday seized a key town along a vital road in Syria's central Hama province, where regime forces are struggling to gain ground despite a month of Russian air strikes.

The setback for Damascus came as France announced it would deploy an aircraft carrier to boost its fight against the Islamic State group, which has seized control of large parts of Iraq and Syria.

Russia sent anti-aircraft missile systems to Syria to back up its air campaign, the commander of the air force Viktor Bondarev said in an interview published Thursday.

"We sent there not just fighter planes, strike aircraft and helicopters but also anti-aircraft rocket systems," Bondarev told Komsomolskaya Pravda tabloid daily.

A coalition including Syrian Arab groups regained a swath of territory in northeastern Syria from Islamic State militants, a U.S. military spokesman said Wednesday, calling it an encouraging success.

The fighters, who are from the Syrian Democratic Forces (SDF) and its Syrian Arab Coalition subgroup, regained 87 square miles (255 square kilometers) near the town of al-Hawl, U.S. military spokesman Colonel Steve Warren said.

A "transition period" in Syria is out of the question because President Bashar Assad is the legitimate leader, the country's deputy foreign minister said on Tuesday.

"There is no transition period. There exist official institutions that are functioning," Faisal Moqdad said on a visit to Tehran, Syria's state news agency SANA reported.

The British government on Tuesday denied it was abandoning plans for a parliamentary vote to join air strikes in Syria as an influential committee of MPs advised against action.

Newspaper reports suggested Prime Minister David Cameron had abandoned plans to seek parliamentary approval to extend missions against the Islamic State jihadist group from Iraq into neighboring Syria.