Opposition factions in Syria will need “several days” to withdraw their heavy weapons from a buffer zone that is being planned in the northwestern region of Idlib, said the Turkish-backed National Liberation Front (NLF) on Sunday. The NLF said that it began withdrawing heavy arms from the zone as part of an agreement between Syrian regime ally Russia and opposition backer Turkey. Two Turkey-backed Syrian opposition officials told Reuters that the removal of heavy weapons began on Saturday. The accord, reached on September 17, aims to stave off a massive regime assault on Idlib, the last major opposition bastion in Syria, by creating a 15 to 20-kilometer (9-12 mile) buffer zone ringing the area. All opposition factions in the demilitarized zone must withdraw heavy arms by Wednesday, and radical groups must leave by October 15, under the deal. "We began to withdraw our heavy weapons from the demilitarized zone to rear positions," NLF spokesman Naji Mustafa told AFP. "The operation will last several days," he said, adding that the weapons will be held by fighters deployed in positions outside the demilitarized zone. The NLF is the main Turkey-backed opposition alliance in the Idlib region, but Hayat Tahrir al-Sham (HTS) holds most of the province and the zone. HTS, led by former al-Qaeda fighters, has yet to announce its stance on the buffer zone deal. On Saturday, a media spokesman for Faylaq al-Sham, one of the NLF factions, confirmed the withdrawal of arms. Seif Raad said it included pulling back missile launchers, tanks and mortars. The Syrian Observatory for Human Rights war monitor said the withdrawal of weapons had already started a week ago and would continue for several more days. Weapons were pulled back in opposition-held areas in the north of Hama province on the border with Idlib and had also been shifted in Idlib province, the Britain-based monitor said. Turkey has deployed troops in "observation posts" it set up in opposition-held areas of Idlib and neighboring Aleppo province in recent weeks.