The UN has called for an urgent de-escalation in north-western Syria, after fighting between government and opposition forces reportedly left dozens of civilians dead or injured.
Secretary General António Guterres urged all parties to recommit to a truce covering opposition-held parts of Idlib, Aleppo and Hama provinces.
Activists said 43 combatants and five civilians were killed on Monday alone.
Two medical facilities were also reportedly damaged by air strikes.
Idlib, northern Hama and western Aleppo make up the last opposition stronghold remaining in Syria after eight years of civil war.
The region is covered by truce brokered in September by Russia, which backs President Bashar al-Assad, and Turkey, which supports the opposition, that has spared the 2.7 million civilians living there from a major government offensive.
A “demilitarised buffer zone” was established along the front line to separate opposition and government forces. Mainstream rebels were required to pull their heavy weapons out of the zone, and jihadists were told to withdraw altogether.
But a takeover of the enclave in January by the jihadist alliance Hayat Tahrir al-Sham, which was known as al-Nusra Front until it broke off formal ties with al-Qaeda in 2016, put the truce deal at risk and was followed by increased hostilities.
Government and Russian forces intensified their air and artillery strikes on opposition-held areas of southern Idlib and northern Hama last month, saying they were attacking jihadist positions in response to repeated truce violations.
What’s the latest?
On Monday, government troops and allied militiamen started to advance on the ground and reportedly captured opposition-held villages in northern Hama. Opposition groups carried out counter-attacks in neighbouring Latakia province.
The Office of the UN High Commissioner for Human Rights (OHCHR) said at least 27 civilians had been killed and 31 injured since 29 April, including many women and children.
The Syrian Observatory for Human Rights, a UK-based monitoring group, put the civilian death toll at 69 and said 41 opposition fighters had also been killed.
OHCHR spokeswoman Ravina Shamdasani said the escalation had also resulted in the displacement of tens of thousands of civilians, three of whom were killed as they fled southern Idlib in a car on 1 May.
What else has been hit?
A series of ground-based attacks and air strikes have been carried out against civilian infrastructure, such as schools and hospitals, causing severe damage, according to Ms Shamdasani.
“We call on all parties to the conflict to respect the international humanitarian law principles of distinction, precaution and proportionality and to ensure the full protection of civilian objects.”
On Monday, the Union of Medical Care and Relief Organizations (UOSSM) said the Al-Amal Orthopaedic Surgical Centre in Kansafra and the Al-Zerba Primary Health Care Centre were damaged by air strikes and put out of service. No injuries or casualties were reported following the attacks.
It said that brought to 12 the number of medical facilities bombed since 28 April.
Another three hospitals were attacked on Sunday despite their co-ordinates having been shared with the warring parties through a UN deconfliction mechanism.
Nine schools have also reportedly been hit since 30 April, and schools in many areas have been closed until further notice, according to the UN.