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Russian jets have carried out a second day of strikes in Syria, with some activists claiming the targets included rebels backed by the United States.
US Senator John McCain said he could "absolutely confirm" that members of the Free Syrian Army (FSA), who had been funded and trained by the CIA, were among those targeted.
Russia's defence ministry said aircraft damaged or destroyed 12 targets in Syria belonging Isis, including a command centre and two ammunition depots, and released two videos of its operations.
Officials acknowledged, however, that other unidentified groups were being targeted as well.
Russian Su-25M and Su-25 jets made 20 attacks between Wednesday and Thursday morning, defence officials said, insisting that civilian areas were not targeted.
The UK-based Syrian Observatory for Human Rights said air strikes in Hama province on Thursday hit FSA members Tajamu Alezzah, and said several civilians and fighters had died.
Russia's air campaign in support of Syrian government forces began on Wednesday in what President Vladimir Putin called a "pre-emptive strike" against terrorists.
His spokesperson, Dmitry Peskov, said Russia was targeting Isis militants as well as a "list" of other unspecified groups.
"These organisations are well known and the targets are chosen in coordination with the armed forces of Syria," he said.
Sergei Ivanov, Mr Putin's chief of staff, had previously said "the operation's target is solely air support for the Syrian government forces in their fight against Isis".
The US Secretary of State, John Kerry, said the government was prepared to welcome Russian military action in Syria as long as it is directed against Isis and al-Qaeda affiliates, but claimed he would have “grave concerns” if it conducted strikes against other groups.
Mr Putin discussed intervention with Barack Obama on Monday as they attended the UN General Assembly in New York, which followed Russia’s transfer of fighter jets and military equipment to Syria.
The leaders agreed on the need to fight Isis but clashed over President Assad after Mr Obama, David Cameron and other global leaders said he must leave to ensure peace in Syria.
Sergei Lavrov, the Russian foreign minister, dismissed claims that moderate rebel groups fighting the regime had been hit, saying Wednesday's strikes “exclusively” targeted Isis.
“Rumours that the targets of these strikes were not Isis positions were groundless,” he added.
Additional reporting by APReuse content