Recapturing the Abu Zuhour air base, which the rebels took in 2015, has been one of the main targets of a major government offensive into Idlib that began in late October. The operations also aim to secure the road linking the capital, Damascus, with the northern city of Aleppo, Syria's largest.
The government-controlled Syrian Central Military Media said on Wednesday that Syrian troops are fighting militants, including members of al-Qaida-linked Levant Liberation Committee, in different areas near Abu Zuhour. The fighting has displaced an estimated 100,000 people who have fled north toward safer areas close to the border with Turkey.
Idlib is the largest remaining territory in rebel hands, and its population is swollen with more than 1.1 million refugees who have fled fighting from other areas in Syria, according to the United Nations. Assad has defeated rebels in many parts of western Syria with critical help from Russian Federation and Iran.
"In Idlib, ground attacks and airstrikes have escalated as a rapidly-moving government offensive gains momentum, jeopardizing the safety of hundreds of thousands of civilians", said Zeid.
Ninety-six civilians, including 27 children, have been killed since December 25 in Syrian or Russian air strikes on Idlib, according to the observatory.
The SCMM and the opposition's Britain-based Syrian Observatory for Human Rights confirmed that 14 villages have been captured over the past hours. The Observatory said the blasts were the result of explosions in an arms depot east of Latakia.
State media said the Syrian army broke through rebel lines Sunday to reach soldiers trapped at the Murakabat vehicle base near Harasta, in the eastern Ghouta suburbs.
The recent military escalation in western Syria has included an unprecedented attack by a squadron of drones on Russian military bases and has cast a shadow over Moscow's efforts to convene a Syria peace congress later this month.
The Observatory said the attacks were carried out by an Islamist rebel faction that operates in rural Latakia province, southwest of, and which had targeted the air base a number of times since December 31.
The official military daily Krasnaya Zvezda said the ministry sent letters to the Turkish military asking it to deploy observers to Idlib to ensure that rebels don't launch more attacks. The reports emerging from Eastern Ghouta of civilian casualties as a result of airstrikes suggest that attacking forces may be failing to abide by the worldwide humanitarian law principles of distinction, proportionality and precautions, raising concerns that war crimes may have been committed.