The Syrian statesman denounced US, French, and Turkish forces operating in his country as "occupying forces" and demanded that they leave immediately.
But the so-called National Liberation Front, a Turkish-backed militant alliance in Idlib, told Agence France-Presse late Sunday that it had raised objections to the deal after meeting with Turkish mentors.
Separate clashes were also taking place in the coastal province of Latakia between militants and government fighters, the Observatory said on Sunday.
"We fully condemn the use of chemical weapons under any circumstances", Moallem said.
The issue has been a flashpoint at the UN Security Council, with Russian Federation vetoing efforts to investigate the Assad regime fully.
Moualem spoke at a time when Syrian government forces, backed by Russian Federation and Iran, have retaken most of the territory rebels seized during the war that has killed over 400,000 people and driven millions from their homes.
The alleged pullback is in line with a plan agreed this month between regime ally Russian Federation and Turkey to avert a large-scale government offensive on Idlib province and surrounding opposition territory, which included setting up a demilitarized zone.
Al Jazeera's Hashem Ahelbarra, reporting from the United Nations, said al-Moallem's "defiant" speech was meant to send a message to both the Syrian opposition and the global community.
The United States has some 2,000 troops in Syria, mainly training and advising both Kurdish forces and Syrian Arabs opposed to President Bashar al-Assad.
During the speech, the Syrian foreign minister mentioned "occupation forces", vowing that the Syrian government will free the country from all "illegitimate foreign troops". But he stressed that it would not accept conditional assistance or help from countries that sponsored the insurgency.
"In one way or another [the worldwide community] all realise that Assad has emerged as the victor, but the future is not guaranteed for any party in Syria", he said. The top diplomat stressed that the doors are all wide open for Syrians overseas to return home.
More than 360,000 people have died and millions displaced from their homes since the regime responded to anti-Assad protests in 2011 with brutal repression.
All conditions are now present for the voluntary return of Syrian refugees, said Muallem.
"We welcome any assistance with reconstruction from those countries that were not part of the aggression on Syria", said al-Moualem, who is also the Deputy Prime Minister.
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