Rome (AFP) - The United States will not cooperate with Russia over air strikes in Syria, Defence Secretary Ashton Carter said Wednesday as Moscow ramped up its bombardments in the war-torn country.

Speaking alongside Italian Defence Minister Roberta Pinotti in Rome, Carter's comments came after the Russian defence ministry said it was considering American proposals to coordinate operations against Islamic State.

"I have said before that we believed that Russia has the wrong strategy –- they continue to hit targets that are not ISIL. We believe this is a fundamental mistake," Carter said, using another name to refer to the Islamic State group.

"Despite what the Russians say we have not agreed to cooperate with Russia so long as they continue to pursue a mistaken strategy and hit these targets."

Before Russia began bombing Syria last week, US officials had said they would welcome "constructive contributions" to the US-led coalition attacking Islamic State jihadists.

But with the Pentagon convinced Russia is focusing on rebels who oppose President Bashar al-Assad, and not IS, military officials see no scope for collaboration.

Moscow claims it is carrying out strikes against IS targets.

Carter's comments followed claims from Russia's defence minister, who said Moscow was considering proposals from the US to coordinate operations against IS.

"The Russian defence ministry has answered the demands of the Pentagon and is examining in depth American proposals on coordinating operations carried out ... against the terrorist group Islamic State on Syrian territory," Russian news agencies cited Igor Konashenkov as saying.

US and Russian officials have held discussions on how to avoid possible accidents with their respective warplanes in action over Syria at the same time.

"What we will do is continue basic, technical discussions on the professional safety procedures for our pilots flying above Syria," Carter added.

"That's it. We will keep the channel open because it's a matter of safety for our pilots."

Story continues

The Pentagon is gravely concerned about the possibility of its pilots or drones crossing path with Russian planes.

A report Wednesday said Russian jets had shadowed a US drone, but a senior defense official downplayed the seriousness of the incident.

"My understanding is that it was not intentional," the official said, noting the jet came within "a handful of miles" of the drone.

- Intensified campaign -

Moscow dramatically intensified its military operations in Syria on Wednesday, with heavy aerial bombing and cruise missile strikes launched from warships in the Caspian Sea that provided cover for a major Syrian army ground offensive in a coordinated attack on rebels.

Russia has said its forces have hit 112 targets since its operations in Syria -- which it insists target IS and other "terrorist groups" -- began on September 30.

But Syrian rebels and their backers say a range of opposition fighters, not just jihadists, have been hit.

Carter was speaking in Rome as part of a five-day European tour aimed at thanking allies who are dealing with emerging threats on NATO's southern flank.

He previously visited Spain and will attend a NATO ministerial meeting in Brussels on Thursday.