1 of 4
Virginia Mayo, Associated Press
U.S. Secretary of Defense Chuck Hagel speaks during a media conference at NATO headquarters in Brussels on Thursday, Feb. 5, 2015. NATO’s chief announced Thursday the alliance is set to more than double the size of its Response Force in response to Russian aggression in Ukraine and the challenge of Islamic extremism. NATO secretary-general Jens Stoltenberg, speaking to reporters before the opening of a meeting of defense ministers, said they were expected to agree to boost the size of the force from 13,000 to 30,000.

BRUSSELS — Defense Secretary Chuck Hagel says he is very concerned about a potential division within NATO as countries in the north want to focus on the growing threat from Russia, while other alliance members in the south are more worried about the influx of foreign fighters from northern Africa.

Hagel says now is the time for unity and wise investments, and NATO must address all of the challenges at the same time.

Hagel spoke as NATO defense ministers gathered in Brussels to discuss ways to reorganize the alliance.

NATO nations have long been split over where the alliance should focus its resources. And the events of the last year, with Russia threatening one NATO flank and Islamic extremists terrorizing the other, has only sharpened that debate.