They have seized "several towns and villages" south of the M4 highway linking the coastal regime stronghold of Latakia to government-held second city Aleppo, it said. State news agency SANA said "units of the Syrian army continued to progress in the south of Idlib" province.
Observatory chief Rami Abdel Rahman said the regime's ultimate aim was to wrest back parts of the M4 still under control of the jihadists and allied rebels. That would require operations against the towns of Ariha and Jisr al-Shughur, both along the M4.
Analysts expect a tough battle for Jisr al-Shughur, held by the jihadist Turkestan Islamic Party whose fighters mainly hail from China's Uighur Muslim minority. They are allied to Hayat Tahrir al-Sham, a group led by Syria's former Al-Qaeda affiliate which dominates the Idlib region.