Russia has conducted more than 50 air strikes since Tuesday against Islamic State (IS) jihadists near the Syrian city of Palmyra, the defence ministry in Moscow said.
"The Russian air force has increased the intensity of its strikes against targets of the armed units of international terrorist organisations near the city of Palmyra," the ministry said in a statement Thursday on its Facebook page.
"Since July 12, Russian air force planes have conducted more than 50 strikes against Islamic State personnel and material in this area."
Six Tupolev bombers flew out of an airbase in Russia on Thursday morning and conducted strikes east of Palmyra, near the cities of Arak and Sukhna, as well as in the Homs region, the statement said.
The ministry said the strikes had destroyed "a command centre, a field camp for IS fighters, two oil processing plants and a large quantity of the enemy's personnel and military hardware."
IS fighters were forced out of Palmyra by Syrian regime forces in March with Russian backing, but Arak and Sukhna remain out of the government's control.
Arak, located 35 kilometres (21 miles) east of Palmyra, is a small town that has strategic importance because of a nearby oil field, while Sukhna, 70 km northeast of Palmyra, is an IS bastion.
Russia is stepping up its bombing campaign in Syria as US Secretary of State John Kerry is set to meet President Vladimir Putin in Moscow on Thursday in Washington's latest bid to revive the stalled Syrian peace process.
Kerry's visit to Russia -- his second this year -- comes as bloodshed continues in defiance of a series of failed ceasefires.
Russia and the US appear increasingly at odds over the way forward amid heightened diplomatic tensions.