DAMASCUS, Jan. 5 (Xinhua) -- A total of 120 rebel fighters have been killed over the past five days of intense battles to stop the advance of the al-Qaida-linked groups in a part of the demilitarized zone in northern Syria, a war monitor reported Saturday.

The slain rebels were killed during the battles between the Hayat Tahrir al-Sham (HTS), the umbrella group of the al-Qaida-linked Nusra Front, and the Turkey-backed rebels of the Nour al-Din al-Zenki, a part of the bigger umbrella of the National Liberation Front, in the western countryside of Aleppo, according to the Syrian Observatory for Human Rights.

The intense battles have so far failed to stop the advance of the HTS and its capture of areas in the western countryside of Aleppo which had been controlled by the Turkey-backed rebels, said the London-based watchdog group.

Notably, the areas that have fallen to the al-Qaida-linked group are part of the demilitarized zones' deal reached between Russian and Turkey last September.

According to the deal, Turkey should have pushed the al-Qaida-linked rebels and those affiliated with terrorist groups out of the zone.

According to the Observatory, the HTS has captured 23 villages and towns from the Turkey-backed rebels.

The report said the fighting has expanded to the northwestern countryside of Aleppo, where the HTS is attacking the Turkey-backed rebels.

The HTS succeeded in capturing the strategic Deir Saman and a citadel bearing the same name, which separates the northwestern countryside of Aleppo from the areas controlled by the Turkey-backed rebels, according to the Observatory.

According to the watchdog, the HTS is "swallowing" other rebel groups, noting that either the Turkish forces or the Syrian government forces could stop the progress of the HTS.

Meanwhile, other activists said the Nour al-Din al-Zenki has dissolved itself after its defeat in western Aleppo countryside and its militants ran to Turkey or the Turkey-controlled Afrin enclave in the northern countryside of Aleppo.