(CNN) Russia's air campaign in Syria has killed hundreds of civilians and caused massive destruction in residential areas, according to a report released Wednesday by Amnesty International.

The rights group claims the pattern of attacks shows "evidence of violations of international law."

Russia has been engaged in a military campaign in Syria in support of embattled President Bashar al-Assad since September. Moscow says its operation is aimed at defeating "terrorist targets" there, but the United States claims the Russian airstrikes are targeting Syrian opposition forces rather than ISIS, which has taken control of large parts of the country.

The Amnesty report, "Syria: Civilian Objects Were Not Damaged: Russia's Statements in Syria Unmasked," singles out six attacks it says took place in the Syrian cities of Homs, Idlib and Aleppo between September and November this year, which claimed the lives of at least 200 civilians and around a dozen Syrian rebel fighters. The group also claimed Russia covered up damage to a mosque in one airstrike, and a field hospital in another.

Doubts over targeting

With an operating base at Hmeymim near Latakia in western Syria, Russia is able to launch as many as 80 sorties per day. There's some doubt among Western analysts about the accuracy of its targeting.

Peter Felstead, editor of Jane's Defense Weekly, told CNN in October that "the air campaign has been effective, but in a typically Russian 'sledgehammer' manner."

"Video released by the Russian MoD, in fact, shows no evidence or precision targeting; some munitions, in fact, looked as if they struck open fields."

David Cenciotti, who runs The Aviationist website, said Russia's Su-24 and 25 bombers have made "significant use of unguided fragmentation bombs ... Su-24s were also seen dropping RBK 500 cluster bombs."

These aren't precision weapons, according to the U.S. military.

But Moscow insists that with aerial reconnaissance by drones and satellite images, the targeting is accurate. In one Moscow briefing, Col. Gen. Andrei Kartapolov said: "There's panic and desertion among [the rebels]. Because of this, we will not only continue with our strikes, but increase their intensity."

Amnesty disagrees.

"Some Russian airstrikes appear to have directly attacked civilians or civilian objects by striking residential areas with no evident military target and even medical facilities, resulting in deaths and injuries to civilians. Such attacks may amount to war crimes," said Philip Luther, director of the Middle East and North Africa Program at Amnesty International.

JUST WATCHED Russia: 320 Syrian militants killed in past 24 hours Replay More Videos ... MUST WATCH Russia: 320 Syrian militants killed in past 24 hours 04:25

"It is crucial that suspected violations are independently and impartially investigated."

Eyewitnesses

Amnesty says its reporting is based on interviews with eyewitnesses and survivors of attacks. The group says it also examined videos and images purportedly showing the aftermath of attacks, supported by the opinion of "weapons experts." Due to the difficulty in obtaining accurate reporting on the ground, Amnesty explained how it determined which attacks were Russian rather than by the other countries carrying out strikes on Syria. Statements from Russia's foreign ministry announcing "terrorist" targets hit were compared with details from the ground about these attacks from witnesses and local activists.

Based on its analysis, Amnesty concluded there were "no military targets or fighters in the immediate vicinity" of the areas targeted. "This suggests that the attacks may have violated international humanitarian law and may, in some circumstances, constitute war crimes," the report said.

In one incident, Amnesty found that five civilians were killed and a dozen homes destroyed by what it suspects was a cruise missile strike launched from a Russian ship. The strike hit residential buildings in Darat Izza, Aleppo, on October 7, it claimed.

JUST WATCHED Russian military warship sends powerful message in Syria Replay More Videos ... MUST WATCH Russian military warship sends powerful message in Syria 02:29

"It felt very different from other airstrikes ... the ground shook like an earthquake ... this was the worst destruction I had seen ... A mother and her two children were killed in one house and a young couple in another house. The couple were married about a week before the attack," Amnesty quoted one local witness as saying. The witness, a local activist, said no one recalled seeing planes flying overhead before the strike. And Russia reported firing 26 miles into Syria that day.

Amnesty also claimed Russia attempted to cover up an attack that hit a mosque in Idlib in October by calling reports of the strike a hoax before issuing a photo it said showed the Omar Bin al-Khattab mosque intact. However, Amnesty said the mosque shown in the photo was different from the one it claimed the Russians struck.

"By presenting satellite imagery of an intact mosque and claiming it showed another that had been destroyed, the Russian authorities appear to have used sleight of hand to try to avoid reproach and avert scrutiny of their actions in Syria. Such conduct does not cultivate confidence in their willingness to investigate reported violations in good faith. Russia's Ministry of Defense must be more transparent and disclose targets of their attacks in order to facilitate assessment of whether they are complying with their obligations under international humanitarian law," said Amnesty's Luther.

Responding to the report, Russian Defense Ministry spokesman Igor Konashenkov said it contained mostly cliches and false information. He denied the use of cluster bombs in Syria.

Konashenkov accused the West of releasing such studies after its own mistakes, pointing to a recent U.S. airstrike in Iraq.

More force

Earlier this week, President Vladimir Putin warned Russia will use more advanced military force against terror groups in Syria "if necessary."

JUST WATCHED Russia uses new device in fight against ISIS Replay More Videos ... MUST WATCH Russia uses new device in fight against ISIS 01:09

"We see how effectively our pilots and intelligence officers work in Syria and how effectively they coordinate their efforts," Putin said at a Kremlin event honoring security service employees, according to the Sputnik state-run news agency.

"At that, they are diversified, and the army, navy and aviation use the most modern weapons," Putin said.

He added: "I would like to note that these are by far not all of our capabilities. We have, by far, not used everything of what we already have. We have additional capabilities. If necessary, we will use them, too."

However, Russia analyst Jill Dougherty described Putin's comments as part "chest-thumping" aimed at a particular audience at home, and perhaps also "a little bit of a shot over the bow" to Turkey.

Relations between the two countries have been tense since the Turkish military downed a Russian bomber in November near the Turkish-Syrian border, after the Turks said they warned the aircraft about violating their airspace. One of the Russian plane's two pilots was killed.