The Syrian Observatory for Human Rights said this was the first such incident since late April.
Syria’s conflict has killed a total of more than 370,000 people.
Ankara has stepped up threats in recent days to launch an offensive against the YPG.
Syrian Observatory for Human Rights says it is unclear what had caused the deadly explosion at the Shayrat airbase.
"I left Syria seven years ago," says Mohammad Hassan. "I don’t know anything about this country."
In the southern province of Daraa, a suicide bomber blows himself up at a military checkpoint, killing six soldiers.
The government began its offensive against the rebel enclave in northwest Syria at the end of April.
In Maaret al-Numan, men covered in blood were carried away from the market by residents and rescue workers.
Syria’s civil war has killed more than 370,000 people and spiralled into a complex conflict since starting in 2011.
The announcement follows talks between UN envoy Geir Pedersen and Foreign Minister Walid Muallem.
Syria’s war has killed more than 370,000 people and displaced millions since it started in 2011.
The corpses include those of people believed to have been executed by the militant Islamic State group.
In Idlib, regime air strikes killed 10 civilians, said the Britain-based Syrian Observatory for Human Rights.
OIC endorsed a UN-backed proposal for a transitional governing body integrating opposition elements in Syria.
The women and children are living among the dregs of the militant Islamic State group in the Kurdish-run Al-Hol camp.
Nine children were among the 21 killed in government fire, says the Syrian Observatory for Human Rights.
"An Israeli missile targeted Tel al Shaar in Quneitra," a Syrian news agency says.
Before IS arrived, Raqqa had more than 20 cultural centres, the largest housing 60,000 books.
The death toll is 10 times the toll the coalition itself has acknowledged.
Among those killed, 13 were civilians, says Britain-based war monitor.
It is “the highest death toll among regime forces since the caliphate was declared defeated”.
Pedersen arrived in Damascus on Saturday, in his third official visit to the country since assuming his post in January.
Veiled women carrying babies and wounded men on crutches hobbled out of the last militant village in eastern Syria.
OPCW says there are “reasonable grounds that the use of a toxic chemical as a weapon has taken place on 7 April 2018."
Syrian president expresses gratitude over Iran's help, Khamenei says "dangerous conspiracies" must be resisted.
Militant IS group has been expelled from all territory it held except for a patch of Baghouz village.
"This battle will be sealed in the coming days," says a spokesperson for Syrian Democratic Forces.
“They are attempting to escape by intermixing with innocent women and children fleeing the fighting,” says US general.
Resolution, adopted by a 70-26 vote, stresses US "faces threats" from terrorist groups in Syria and Afghanistan.
There are no easy answers.