Most Islamic State fighters who had joined the terror group from the Russian North Caucasus region of Chechnya have been killed, Chechen leader Ramzan Kadyrov told Russian news site Tass Wednesday. The militant group also known as ISIS had been recruiting heavily from the predominately Muslim part of southern Russia in efforts to tap into potential recruits' extensive military experience that was gained in regional wars between Russia and Chechnya in the 1990s.

"We contributed to this so that they do not return back to the republic and spill blood of innocent people," said Kadyrov, who was referring to recent Russian airstrikes that have targeted ISIS in recent weeks. "We also helped many young people to come from Syria back to [a more] peaceful life."

Kadyrov has been aggressively opposed to the Islamic ideologies of the Syria and Iraq-based terror group. Last month, as Russian forces began hitting ISIS and Syrian rebel targets inside Syria, Kadyrov offered to send thousands of his Chechen fighters to take part in a ground offensive against ISIS.

Russia became militarily involved in Syria after its aircraft and ships began arriving in the country early last month. While Moscow claimed that its only aim was to provide weapons in support of Syrian President Bashar Assad's authoritarian regime, airstrikes against ISIS and other groups opposed to the Assad's leadership began two about a month later.

Since then, Russia and the U.S., which is also conducting bombing raids against ISIS, have disagreed about the best way to combat the terror group. The Pentagon had said it would work with Russia to hit ISIS, but not while Moscow insisted on supporting Assad, according to a Defense News report.

Adding to the frayed relations between the two, Kremlin jets have been violating NATO- member Turkey's airspace. NATO, of which the U.S. is a key member, said it would support Turkey against further Russian aggression.

"Turkey is a strong ally and they have the second-largest army," Stoltenberg told Reuters. "They have a capable air force, so the Turkish armed forces are the first responders, but NATO is there to help and assist them if they need."

The Syria war, which began in early 2011, has seen more than 250.000 people killed and over four million displaced.