US will target IS 'aggressively across every front': Obama

US President Barack Obama has said the United States would keep targeting the Islamic State group "aggressively across every front."

Speaking to reporters after meeting with security and military officials, the president acknowledged that pressure against the group had prompted the jihadists to increase attacks outside Syria and Iraq, such as in the United States, France and Turkey.

"As we have seen, it is difficult to prevent small cells of terrorists willing to kill the innocent and (who) are willing to die. We will keep going after them aggressively across every front of this campaign," he said at a Pentagon news briefing.

Obama also expressed concern about Russia's military action in support of the Syrian regime, and urged Moscow to cooperate with Washington to find a way out of the crisis.

"The US remains prepared to work with Russia to try to reduce the violence and strengthen our efforts against ISIL, Al-Qaeda and Syria. But Russia has failed to take the necessary steps. Given the deteriorating situation, it is time for Russia to show it is serious about pursuing these objectives," he said.