Syrian army and allied forces supported by Russian warplanes made further advances as they pressed an offensive against insurgents on Monday, in the fiercest clashes for nearly a week, a monitor said.

Russian jets carried out at least 30 air strikes on the town of Kafr Nabuda in Hama province in western Syria, and hundreds of shells hit the area as the Syrian army and Hezbollah fighters seized part of it, the Syrian Observatory for Human Rights said.

Forces loyal to President Bashar al-Assad have in the past few days recaptured territory close to the government's coastal heartland in the west thanks to Russia's intervention, reversing rebel advances made earlier this year.

Moscow says its air campaign targets Islamic State, but most of the strikes have hit rival insurgent groups fighting against Assad, some of which are supported by the United States.

Pro-government forces including the Lebanese group Hezbollah on Monday captured the southern part of Kafr Nabuda, the Observatory's Rami Abdulrahman said.