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 so-called Syrian Observatory for Human Rights said.
Ground attacks using heavy surface-to-surface missile bombardments targeted at least four militant positions in the area and there were heavy clashes on the ground, the head of the group Rami Abdulrahman said, according to Reuters.
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 militant-held areas.
Reuters reported last week that allies of Syrian President Bashar al-Assad were preparing a ground attack in Syria, aimed at recapturing territory lost by the government to militants in rapid advances this year.
Abdulrahman, who tracks the conflict using sources in Syria, said the ground assault was being carried out by Syrian army and their allies, with no immediate sign of Russian involvement on the ground.
Russia, a top ally of Assad, started air strikes in Syria a week ago, saying they were targeting hardline the Islamic State in Iraq and the Levant militants.
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 so-called Syrian Observatory for Human Rights said.
Most of Idlib province is held by an militant alliance that includes al Qaeda's Syria wing Nusra Front and other extremist factions.