The bombing raids hit a string of towns and villages in the northwest province of Idlib, which is nearly entirely controlled by various jihadist and hardline rebels.
Elsewhere in Syria, he said the numbers of people stuck in besieged or other areas humanitarian workers can not easily access has shrunk dramatically since a year ago to just over two million people.
Moumtzis called on the guarantors of the detente zones in the Arab country, Russia, Turkey and Iran to intensify their commitment to maintaining the ceasefire in effect, especially in the northwestern province of Idlib, where "2.5,000,000 civilians are increasingly moving towards the Turkish border", their last means of escape, he said.
"Hayat Tahrir al-Sham (HTS) began heavily shelling the two villages, and broke into Fuaa to attack local fighters", said Observatory chief Rami Abdel Rahman.
The fighting, which was continuing Sunday, had killed six Syrian pro-regime fighters and at least three from HTS.
Fuaa and Kafraya are the only two places in Syria now designated as besieged by the United Nations.
The villages are home to an estimated 8,100 people, a lot of them Shiite Muslims.
Deadly clashes as jihadists attack besieged Syria regime villages
On Friday, Russian Defense Ministry rebutted allegations of an airstrike carried out by a Russian warplane on June 7 near the village of Zardana in Syria's Idlib province.
Last year, Turkey, Iran and Russian Federation agreed in Astana to establish de-escalation zones in the northern province of Idlib and parts of neighboring Latakia, Hama and Aleppo.
Panos Moumtzis, UN Regional Humanitarian Coordinator for the Syria Crisis, shows a Syria's map to the media during a press conference on humanitarian access in Syria, during a press conference, at the European headquarters of the United Nations in Geneva, Switzerland, Monday, June 11, 2018. "There is no other location to move them to [in Syria]", he told a news briefing in Geneva.
The situation inside Syria's Idlib threatens to become "highly explosive" amid an uptick in the conflict between armed groups and a spike in the number of people displaced inside the war-torn country, a top United Nations aid official said on Monday.
HTS and its allies control around 60 percent of the province, its local rivals hold about a third, and the regime controls about ten percent, according to the Observatory.
More than 350,000 people have been killed since the Syrian conflict erupted in 2011 with the brutal repression of anti-government protests.
Sane Trilogy Gets Future Tense On June 29, 2018
The level is allegedly based on the design of an unreleased level from the original game called Waterfall. Sane Trilogy , fans on new platforms will also receive Stormy Ascent as a bonus level starting June 29th.
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