"But so are they" he said, meaning the Assad regime.
Turkish President Tayyip Erdogan said the military operations in Afrin and Idlib would continue, and repeated Turkey's demand for USA forces to pull back from the town of Manbij where they are stationed alongside Kurdish-led forces.
The UN officials said civilians in Idlib were being forced to move repeatedly to escape fighting, and warned that the province - home to 1.16 million displaced people - might not be able to withstand the consequences of continued conflict.
The Syrian Observatory for Human Rights said Tuesday's bombardment of Eastern Ghouta had killed at least 41 people.
On January 22, 2018, at least 21 people, including children, suffer breathing difficulties in a suspected regime chemical attack in a besieged rebel enclave near Damascus, the Observatory says.
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The air defenses had been sent to frontlines with militants in rural areas of Aleppo and Idlib.
The SOHR and state media also said that shells fired by rebels in the Eastern Ghouta had killed three people in government-held parts of Damascus.
"They (the U.S.) tell us don't come to Manbij, but we will come to Manbij to hand over the land to its original Arabic owners", Erdogan said in a speech to his ruling Justice and Development Party's parliamentary group in Ankara.
Iran, Turkey and Russian Federation brokered the Astana dialogue on Syria and the first five rounds of the talks were held on January 23-24, February 15-16, March 14-15, May 3-4 and July 4-5, 2017.
Iran urged Turkey on Monday to halt its two-week-old military offensive against the Kurdish YPG militia in northern Syria's Afrin region, which is adjacent to Idlib.
A joint investigation team comprising experts from the United Nations and the Organization for the Prohibition of Chemical Weapons concluded that the Syrian government used chlorine gas in at least two attacks in 2014 and 2015 and used the nerve agent sarin in an aerial attack on Khan Sheikhoun last April that killed about 100 people and affected about 200 others.