A Russian air force helicopter is pictured on the tarmac of Heymim air base near the Syrian port town of Latakia.

Reuters/Beirut

The Syrian army and allied militia carried out ground attacks on insurgent positions in Syria on Wednesday backed by Russian air strikes, in what appeared to be their first major co-ordinated assault since Moscow intervened last week, a monitor said.

Russia's air strikes hit northern parts of Hama province and nearby areas in Idlib province, targeting towns close to the main north-south highway that runs through major cities in western Syria, the Syrian Observatory for Human Rights said.

Ground attacks using heavy surface-to-surface missile bombardments targeted at least four insurgent positions in the area and there were heavy clashes on the ground, the head of the Observatory Rami Abdulrahman said.

Although Wednesday's combined assault marked a military escalation, it was not immediately clear whether there would be rapid gains in a conflict that has already dragged on more than four years.

"There is no information yet of any (government) advances on the ground, but the air strikes have hit vehicles and insurgent bases," Abdulrahman said.

A regional source familiar with the military situation in Syria said forces including Hezbollah fighters were taking part in the ground attack against four rebel-held areas.

Reuters reported last week that allies of Syrian President Bashar al-Assad, including Iranians, were preparing a ground attack in Syria, aimed at recapturing territory lost by the government to rebels in rapid advances this year.

Abdulrahman, who tracks the conflict using sources in Syria, said the ground assault was being carried out by "regime forces" and their allies, with no immediate sign of Russian involvement on the ground.

Syrian state media and regional pro-government channels made no mention of new Russian strikes or the ground attacks on Wednesday.

Russia, a top ally of Assad, started air strikes in Syria a week ago, saying they were targeting hardline Islamic State militants.

But fighters on the ground and Western countries have said the Russian campaign is mainly focusing on other rebel groups that have seized government-held areas in the west, and is aimed at shoring up Assad rather than combating hardliners.

Russia's strikes on Wednesday targeted the towns of Kafr Zita, Kafr Nabudah, al-Sayyad and the village of al-Latamneh in Hama province and the towns of Khan Shaykhun and Alhbit in Idlib, the Observatory said.

Most of Idlib province is held by an insurgent alliance that includes al Qaeda's Syria wing Nusra Front and other Islamist factions.