Russia's airstrikes in Syria could continue for three to four months, according to the head of the lower house of the Russian parliament's foreign affairs committee, as controversy continues over what Moscow's attacks are actually targeting.

"There is always a risk of being bogged down but in Moscow, we are talking about an operation of three to four months," Alexei Pushkov told French radio Europe 1, adding that the strikes were going to intensify.

Officials announced on Friday that airstrikes had been carried out for a third day in row and claimed that these hit 12 Islamic State (IS) targets.

Yet the US, which is leading its own air campaign against IS, says Moscow has been using its campaign as a pretext to hit other groups opposed to Russia's ally, President Bashar al-Assad.

Some of the groups that have been hit are supported by countries which oppose both Assad and IS, including at least one group that received training from the CIA.

Russia's air campaign in a country already being bombed by a US-led coalition of Western and Arab countries means that the Cold War superpower foes Moscow and Washington are now flying combat missions over the same country for the first time since World War II.

Russian Su-34, Su-24M, and Su-25 warplanes flew 18 sorties, hitting a command post and a communications center in the province of Aleppo as well as a militant field camp in Idlib, a Defense Ministry statement said. A command post in the province of Hama was also completely destroyed, it added.

The UK-based Syrian Observatory for Human Rights, which monitors the conflict with a network of sources on the ground, said IS had no presence in the western and northern areas that were struck.

This comes as Russian President Vladimir Putin is in Paris where he is expected to meet with French President Francois Hollande and German Chancellor Angela Merkel.

The governments of France, Germany, Qatar, Saudi Arabia, Turkey, United Kingdom, and United States released a statement on Thursday expressing "deep concern" about the strikes.

"These military actions constitute a further escalation and will only fuel more extremism and radicalization."

Russia began airstrikes in Syria on Wednesday in a major escalation of the more than four-year conflict, hitting rebel groups in the country's west, including Homs province. Local activists also claimed then that rather than targeting IS, the strikes hit rebel positions in Talbiseh and elsewhere.

The head of Syria's main opposition group said that dozens of civilians, including children, have allegedly been killed in the first wave of Russian airstrikes — claims that have been rejected by Moscow.

"The Russians struck northern Homs today and killed 36 innocent people… Who fought against extremism," said Khaled Khoja, head of the National Coalition, in an interview.

"It's obvious today's attack on civilians showed clearly that the Russians' aim [is] not to fight ISIS [or IS], it's to prolong the life of the Syrian regime," he added.

On Thursday, two members of a rebel brigade operating in Talbiseh told VICE News via phone that fast jets of a kind they'd never seen before hit the town between 1pm and 2pm (local time) causing dozens of casualties including civilians and children.

"The regime has bombed this area many times before, but not heavy like yesterday," one said, adding that the attack was of a severity they hadn't experienced before. "We didn't guess that it would be this strong. We knew there would be bombing from Russia, but we didn't think it would be like this."