US President Barack Obama has warned Russia that its bombing campaign to support Syrian President Bashar al-Assad will suck Moscow into a quagmire that will be hard to get out of.
Obama said Russia was also failing to distinguish between Islamic State of Iraq and the Levant (ISIL) fighters and more moderate rebels in Syria.
"An attempt by Russia and Iran to prop up Assad and try to pacify the population is just going to get them stuck in a quagmire and it won't work," Obama told a White House news conference on Friday.
"From their perspective, they're all terrorists. And that's a recipe for disaster."
Russia continued bombing Syria on Friday for a third straight day. Targets have included ISIL's main stronghold in Raqqa, but also the provinces of Hama, Aleppo and Idlib where few ISIL fighters operate.
Obama said he would not turn the Syrian civil war into a "proxy war" between the US and Russia. "This is not some superpower chessboard contest," he said.
Fresh Russian attacks
Russian President Vladimir Putin's decision to launch strikes on Syria marks a dramatic escalation of foreign involvement in a more than four-year-old civil war in which every major country in the region has a stake.
Earlier, Russia said it had launched fresh air strikes against ISIL in Syria.
The Russian defence ministry said that the latest strikes targeted a facility used to produce explosive devices near the city of Maarat an Numan in Idlib province, as well as a nearby "terrorist" base.
An underground command post had been destroyed in a strike in Latamna, in Hama province, it said.
"Six strikes were conducted on targets of the ISIL terrorist group in 14 flights," the defence ministry said in a statement on the third day of its military intervention.
At least 12 members of ISIL group were killed in Russia's first air strikes on Raqqa, the UK-based Syrian Observatory for Human Rights said on Friday.
Activists and residents of the city said ISIL had cancelled Friday prayers and emptied mosques there, fearing further attacks.
"The residents are very afraid, especially if the Russians are going to operate like regime planes by targeting civilians," said activist Abu Mohammad from Raqqa.
On Thursday, Russian jets hit areas in the suburbs of Hama and Idlib, all areas under the control of loose coalitions of rebel groups, including the Western-backed Free Syrian Army.
Activists on the ground told Al Jazeera that the majority of the attacks hit civilian targets, a claim that Moscow denies.
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The US-led coalition said it conducted 28 air strikes on ISIL targets in Syria and Iraq on Thursday.
Washington and its allies have asked Russia to stop its strikes on targets other than ISIL, as Russia's lower house said the air strike campaign over Syria could last three to four months.
Putin told French counterpart Francois Hollande in Paris on Friday that Russian actions in Syria were aimed at fighting "ISIL, al-Nusra Front and others," Kremlin spokesman Dmitry Peskov told Russian news agencies.
Meanwhile, the Syrian Observatory for Human Rights, a UK-based activist group, said government helicopters had dropped barrel bombs on the city of al-Bab on Friday, killing dozens of people and injuring many others.
Syria ready for talks
Also on Friday, Syria's foreign minister said that his country will join preliminary UN peace talks.
Walid al-Muallem said that he understood the talks, proposed by UN envoy Staffan de Mistura, are "mainly to exchange ideas" and are non-binding.
"I would like to announce here that Syria agrees to participate in the four brainstorming committees of experts proposed by the special envoy Staffan de Mistura," he told the 193-nation assembly.
Muallem later questioned the value of political negotiations and said air strikes against fighters in his country are useless if they are not coordinated with his government, adding that Russia's air strikes have received the country's support.
Obama, who met Putin at the UN earlier this week, said he was willing to work with Moscow to broker a political solution that involved the Syrian president stepping down, but would not cooperate with a Russian campaign that targets the moderate opposition.
Meanwhile, the UN said it had been forced to suspend planned humanitarian operations in parts of Syria due to the fighting.
More than four million people have fled the Syrian conflict, with hundreds of thousands heading to Europe, which is now facing its worst migrant crisis since World War II.