Britain-based war monitor Syrian Observatory for Human Rights says over 60 Syrian regime fighters have been killed in 48 hours.
Militants have killed more than 60 Syrian regime fighters in 48 hours, a monitor said Saturday, in some of the deadliest attacks on pro-Damascus forces in recent weeks.
YPG-led SDF in March announced the defeat of the Daesh's "caliphate" in eastern Syria, but the terrorists have retained hideouts there and in other parts of the country as well as the ability to carry out deadly assaults.
The YPG is the Syrian offshoot of the PKK terrorist organisation.
Turkey, the US and the EU recognise the PKK as a terrorist organisation.
Since Thursday, Daesh militants have killed 35 pro-Damascus fighters in regime-held parts of central and eastern Syria, the Syrian Observatory for Human Rights said.
Observatory chief Rami Abdel Rahman said it was "the highest death toll among regime forces since the caliphate was declared defeated" in the eastern village of Baghouz last month.
Regime fighters also came under attack on another front of Syria's grinding eight-year war, the Britain-based monitor added.
On Saturday, terrorists linked to Syria's former Al Qaeda affiliate attacked loyalists outside the northwestern region of Idlib, killing 26 pro-Assad fighters, it said.
It was the latest death tally in a civil war that has killed more than 370,000 people since starting in 2011 with the brutal repression of anti-government protests.
Regime leader Bashar al Assad has managed to claw back around 60 percent of the country with Russian military backing since 2015, but several regions remain beyond the regime's control.
These include a large swathe of northeastern Syria held by YPG who have been fighting Daesh with the support of a US-led coalition, as well as the region of Idlib held by Syria's former Al Qaeda affiliate.
Regime forces, in theory, control the vast desert that stretches from the capital Damascus to the Iraqi border, but Daesh is still present there.
Since Thursday they have killed 27 troops and allied militiamen, including four Syrian regime officers, in the desert east of Homs province, the Observatory said.
Daesh claimed the attacks.
The Observatory also said Daesh militants killed another eight soldiers and militiamen in the eastern province of Deir Ezzor on Thursday night.
That attack targeted a desert village south of the city of Mayadeen on the Euphrates River, upstream from Baghouz.
Daesh swept across a large swathe of Syria and Iraq in 2014, declaring a cross-border "caliphate" in territory that was once roughly the size of the United Kingdom.
But after various military operations in both countries, Daesh lost the last shred of its proto-state on the eastern banks of the Euphrates last month.
The US-led coalition has however repeatedly warned that the battle against the militants is not over.
Saturday's attack by a Hayat Tahrir al Sham (HTS) affiliate on the western edges of Aleppo city killed 21 loyalists while an ambush by HTS-linked terrorists took the lives of five more pro-regime fighters in the northeast of Latakia province.
On Friday, Assad urged progress on removing "obstacles" to the stalled Idlib deal ahead of talks to be attended by Russia, fellow ally Iran, and Turkey next week in Kazakhstan.
And on Saturday, he met Russian Deputy Prime Minister Yuri Borisov in Damascus for talks, including on ways to overcome obstacles resulting from international sanctions imposed on Syria, the regime said.