????BRUSSELS, Otc. 8 (Xinhua) -- NATO defense ministers on Thursday agreed to take further steps to make the Alliance's collective defense stronger and also expressed their serious concern over Russia's military activity in Syria at a meeting.

????NATO Ministers gave green light to the completed military concept for the Enhanced NATO Response Force, which will count up to 40,000 troops, twice as the current level.

????"We now have everything in place to make the Response Force stronger, faster and more capable," said NATO Secretary General Jens Stoltenberg at the press conference following the meeting.

????The Ministers also agreed to set up two more NATO Force Integration Units (NFIUs) or small headquarters in Hungary and Slovakia to ensure the fast deploying of NATO forces.

????The units are not military bases, but they are part of the Readiness Action Plan, the biggest reinforcement of NATO's collective defense since the end of the Cold War. Six other NFIUs have been activated in September in Bulgaria, Estonia, Latvia, Lithuania, Poland and Romania.

????The defense ministers also held a discussion on Syria after NATO denounced Russia for violating Turkish airspace during its air campaign in Syria.

????NATO has held an emergency meeting of ambassadors from its 28 member states in Brussels to respond to this Monday. In a statement the bloc said the military actions by Russia in and around Syria are unacceptable.

????Stoltenberg pointed out that "NATO is able and ready to defend all Allies, including Turkey against any threat" ahead of the Thursday's meeting, saying NATO will respond to the challenges both to the east and south.

????"We see an escalation of Russian military activity in Syria. And the ministers agreed that Russia's military escalation in Syria raises serious concerns," said NATO chief at the press conference.

????He called on Russia "to play a constructive role in the fight against ISIL," adding that NATO stands in strong solidarity with Turkey, which became a member of the Alliance since 1952.

????"NATO supports the efforts by the UN and others to try and find a political negotiated solution to the crisis," Stoltenberg said.

????Russian Defense Ministry on Monday blamed bad weather conditions for the brief violation of Turkish airspace by a Russian aircraft near Syrian border.

????"The incident was a consequence of unfavorable weather conditions in the area. One should not look for any conspiracy theories here," the ministry said.