At least 20 people have been killed by Syrian security forces in the north-western town of Khan Sheikhoun during a visit by UN observers, activists say.
Unconfirmed reports say the deaths occurred when security forces opened fire on a funeral procession in the town in Idlib province.
Three of the monitors' cars were damaged in a blast in the town, but the observers were not hurt, the UN said.
This comes despite the UN-backed ceasefire in place since last month.
The Syrian government has so far not publicly commented on the incidents.
In a separate development, the head of Syria's election committee announced that turnout in last week's parliamentary elections was more than 50%.
The committee did not say who had won, but it is clear that the ruling Baath party has secured a substantial majority of the seats, the BBC's Jonathan Head in neighbouring Turkey reports.
This was the first election in which the Baath party was not, in theory, guaranteed a majority, our correspondent says.
Opposition parties - which boycotted the election - have dismissed the vote as a sham.
As the parliament's powers are poorly defined, he adds, there was no chance that the poll would dilute President Bashar al-Assad's power, our correspondent says.