Turkish guards have killed eight Syrian civilians, including four children, while they were trying to cross the Turkish border from their war-torn country, a monitoring group reported on Sunday.
The incident occurred Saturday night in Idlib in north-western Syria near the Turkish border, the Syrian Observatory for Human Rights said.
The watchdog added that the latest deaths raised to 60 the number of civilians who have been killed by Turkish guards while trying to enter Turkey this year. They included eight children.
There was no official Turkish comment. The Turkish-backed Syrian opposition leadership body, the National Coalition, said it had requested a clarification and steps to ensure there was no repetition of the incident.
Turkey claims it has an open-border policy for Syrians. However, the process of getting into Turkey is highly selective, and tens of thousands of people are stranded on the Syrian side.
Turkey hosts more than 2 million Syrian refugees.
In April, Human Rights group Amnesty International reported that Turkish security forces had shot and injured civilians, including children, who "out of desperation have attempted to cross the border unofficially with the help of smugglers."
Turkey backs rebels who are fighting to oust the regime of Syrian President Bashar al-Assad.
Jets operated by al-Assad's forces and their Russian allies on Sunday stepped up the bombardment of an Islamic State-held city in northern Syria, increasing pressure on the extremist militia, the observatory reported.
The warplanes have carried out at least 18 airstrikes since dawn on the city of al-Tabqa, just west of al-Raqqa, Islamic State's de facto capital in Syria, according to the Britain-based watchdog.
At least 10 civilians were killed and dozens injured in the strikes, according to the observatory, which relies on a network of activists inside Syria.
Eight Islamic State militants and nine pro-government fighters were also killed.
The bombing has prompted a mass exodus of locals from the city to safer areas.
Earlier this month, Syrian troops started an offensive aimed at cutting off al-Raqqa from the Turkish border.
Troops and militiamen, backed by Syrian and Russian warplanes, pushed east from the regime outpost of Ithriya, closing in on Tabqa.
On Sunday, regime forces and allied militiamen advanced within less than 7 kilometres of Tabqa's military airport that Islamic State seized in 2014, the observatory said.
The Kurdish-led Democratic Forces of Syria (DFS), backed by US airstrikes, are also pushing towards Tabqa, located near Syria's largest dam, at the southern end of Lake Assad on the Euphrates.
The DFS, an alliance of Kurds and Arabs, are meanwhile pressing ahead with an offensive aimed at retaking the northern Syrian town of Minbij from Islamic State.
Minbij is strategically important as it controls a supply route from the Turkish border to al-Raqqa.
Clashes between DFS forces, backed by a US-led air power, and militants were under way Sunday on the outskirts of Minbij, the observatory said. Some 800 civilians fleeing the town had reached DFS-held territory safely, the watchdog added.
West of Minbij, the observatory reported that Islamic State fighters had rounded up 200 young men in the village of al-Kawakli, raising fears that they were being sent to fight on the nearby front lines.
Minbij has been under Islamic State control since 2014.
In recent months, the al-Qaeda splinter group has suffered military setbacks and lost ground in Syria and neighbouring Iraq.