President Vladimir Putin has defended Russia's military operations in Syria, saying the aim is to "stabilise the legitimate authority" of Syrian President Bashar al-Assad.
Russia wants to "create conditions for a political compromise" in Syria, he told Russian state TV.
On Monday the EU's foreign affairs chief, Federica Mogherini, called Russia's role "a game-changer". She said: "It has some very worrying elements."
EU ministers are discussing Syria now.
Going into the Luxembourg meeting, several foreign ministers stressed that air strikes should only target so-called Islamic State (IS) fighters and other Islamist "terrorists".
The US and UK governments have accused Russia of attacking mainly "moderate" anti-Assad groups, rather than the jihadists.
Mr Putin denied that that was the case. .
"The interventions against Daesh (IS) have to be clearly against Daesh and other terrorist groups, as defined by the UN," Ms Mogherini stressed.
Luxembourg Foreign Minister Jean Asselborn also said "the target is IS and nothing else".
Ms Mogherini said she was especially worried about recent violations of Turkish airspace by Russian jets.
Syrian forces are said to have made significant advances against rebels.
Government gains in Idlib, Hama and Latakia provinces were on Sunday reported both by the Syrian government and opposition activists.
The main battlefront is currently close to the key highway that links the capital with other major cities, including Aleppo. Mr Assad's forces are believed to be seeking to cut off rebels in Idlib.
Russia's security services said on Monday they had arrested a group of Russian citizens with links to IS.
The FSB security agency said in a statement that some of those detained had been through IS training camps in Syria and were suspected of planning a terror attack.
Explosives and bomb-making equipment were found at an address in Moscow used by the suspects, the agency said.
Speaking to Rossiya One TV on Sunday, Mr Putin said that without Moscow's support for President Assad, there was a danger that "terrorist groups" could overrun Syria.
Mr Assad's government was currently "under siege", he said, adding that militants were "at the edge of Damascus".
He also urged other nations to "unite efforts against this evil (terrorism)".
The US-led coalition - which has been carrying out its own air strikes in Syria - earlier said it would not be co-operating with Russia.
Several countries - including the UK and Turkey - have described Russia's support for President Assad as a "mistake".
Russia said on Sunday its aircraft had carried out more than 60 missions over Syria in the past 24 hours, and that IS was its main target. The attacks began on 30 September.
When asked whether the EU would have a dialogue with Mr Assad, Ms Mogherini stressed EU support for UN efforts to mediate, but did not rule out including Mr Assad in transitional talks.
"We say we have to have all the relevant actors round the table," she said.
Analysis: Jim Muir, BBC News, Beirut
Government forces are basically trying to win back areas they lost earlier this year, to the north of the city of Hama, and in the northern mountains of Latakia province near the coast. Rebels had penetrated there after unifying their ranks and with more concerted backing from their outside supporters, Turkey, Saudi Arabia and Qatar.
That posed a real threat to the heartland of Bashar al-Assad's regime, and it is almost certainly what triggered the Russian intervention and a stepped-up role by Iran.
A senior commander of the al-Nusra Front, the al-Qaeda affiliate which has forces in the area, has issued a call to all the rebel groups to unify and launch a co-ordinated counter-attack on all fronts.
He said if the rebels lost the initiative to the regime and the Russians, they would suffer a series of collapses and their future would be bleak.
Syria's civil war
Why is there a war in Syria?
Anti-government protests developed into a civil war that four years on has ground to a stalemate, with the Assad government, Islamic State, an array of Syrian rebels and Kurdish fighters all holding territory.
What's the human cost?
More than 250,000 Syrians have been killed and a million injured. Some 11 million others have been forced from their homes, of whom four million have fled abroad - including growing numbers who are making the dangerous journey to Europe.
How has the world reacted?
Iran, Russia and Lebanon's Hezbollah movement are propping up the Alawite-led Assad government, while Turkey, Saudi Arabia and Qatar back the more moderate Sunni-dominated opposition, along with the US, UK and France. Hezbollah and Iran have pro-Assad forces on the ground, while a Western-led coalition and Russia are carrying out air strikes.