Russia said its planes had flown 64 sorties, striking 63 targets and destroying 53 fortified positions in the previous 24 hours. As in the past, it described all targets as belonging to Islamic State, although most of the areas it said it had struck are not held by that group.
Syrian state television also reported that the government had captured Tal Skik with the help of Russian air strikes.
However, the advance came at a cost, with the Observatory and a Lebanese television station reporting that a senior Hezbollah commander had been killed fighting on the Syrian government side.
In recent days, Russia has dramatically intensified its 10-day-old bombing campaign. Moscow says it is targeting the Islamic State militant group, but most of its strikes have hit other rebel factions fighting against Assad, some of which have the support of Gulf Arab powers, Turkey or the United States.
The Russian bombing has been accompanied by a major advance by Syrian government forces, backed by thousands of Lebanese Hezbollah militiamen and hundreds of Iranian troops.
Putin's meeting with Riyadh's Defence Minister Mohammed bin Salman, a son of the Saudi king and leading figure in its regional security policy, was the Kremlin's boldest move to reach out to Assad's foes since launching the strikes.
After the meeting, which took place on the sidelines of a Formula One Grand Prix race in the Russian resort of Sochi, Foreign Minister Sergei Lavrov said Moscow had sought to assuage Riyadh's concerns. Both sides shared the objective of preventing a "terrorist caliphate" from taking root in Syria, he said.
Foreign Minister Adel al-Jubeir said Saudi Arabia, which along with other Arab states has joined a U.S.-led coalition bombing Islamic State in Syria and Iraq, was still demanding Assad's removal from power. He hoped talks with Russia would continue.
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Putin also met Abu Dhabi's Crown Prince Mohammed bin Zayed Al Nahyan, who holds a senior post in the armed forces of the United Arab Emirates, another rich Gulf state hostile to Assad.
Turkey, a NATO member that has accused Russian aircraft of violating its air space during the bombing campaign, said Syrian jets and missile systems had harassed its fighter planes at the border on Saturday in the latest incident.
Moscow said its officials had held a second video conference with counterparts from the United States to ensure safety as the former Cold War foes both fly combat missions in the same air space for the first time since World War Two.
The Russian intervention has upended the strategy of the U.S. administration of President Barack Obama, which has led a separate bombing campaign against Islamic State for a year but failed to establish strong ties with fighters on the ground.
Washington and Moscow say they have the same enemy in Islamic State, the world's most violent jihadist group, which has set up a caliphate in much of eastern Syria and northern Iraq. But they have very different friends.
Washington and its European and Middle Eastern allies say the Syrian president should step down in any peace deal, while Moscow says his government should be the centerpiece of international efforts to fight extremism.
Washington has announced in recent days that it is abandoning a failed effort to train "moderate" rebel groups opposed to both Assad and Islamic State.
Other rebels fighting against Assad are equipped and trained by Washington's Arab allies and range from secular nationalists to Islamist militants affiliated with al Qaeda.
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Moscow accuses Washington of effectively siding with other militants that are no different from Islamic State; Washington says the Russian campaign helps Islamic State by targeting its rivals.
In recent days, Islamic State fighters have taken advantage of the Russian attacks on rival rebel groups to advance near Aleppo in the north of Syria, the Observatory and sources on the ground say. The Observatory said there was fighting on Sunday between Islamic State and other rebels in that area, although no change in positions since Saturday.
In neighboring Iraq, the army said it had struck a convoy carrying Islamic State's leader Abu Bakr al-Baghdadi to a meeting of Islamic State figures. Local residents in the town of Karabla near the Syrian border said eight Islamic State leaders had been killed in an air strike, but Baghdadi did not appear to be one of them.