Russian President Vladimir Putin said Friday it was premature to talk about Russia taking part in military operations against the Islamic State group, as the US said it was checking reports of Russian troops in Syria.

Asked whether Russia could take part in operations against IS, Putin said: "We are looking at various options but so far what you are talking about is not on the agenda."

"To say we're ready to do this today -- so far it's premature to talk about this. But we are already giving Syria quite serious help with equipment and training soldiers, with our weapons," RIA Novosti state news agency quoted Putin as saying.

The White House on Thursday said it was closely monitoring reports that Russia is carrying out military operations in Syria, warning such actions, if confirmed, would be "destabilising and counter-productive."

The comments come after images appeared on a social media account linked to Syrian fighters purporting to show Russian aircraft and drones near Idlib province.

Putin, speaking at an international economic forum in the far eastern city of Vladivostok, criticised US air strikes on IS as ineffective.

"So far the effectiveness of these air strikes is low," he said.

Putin said that military supplies to Syria were fulfilling contracts dating back five to seven years.