Updated

The world may be a riskier place nowadays, but overall spending on defense among NATO's member countries is expected to be lower this year than in 2014, the alliance said Monday.

U.S. President Barack Obama and other NATO leaders last fall committed their countries to hike defense spending over time to 2 percent of gross domestic product. But NATO Secretary-General Jens Stoltenberg said alliance estimates now show only five nations will hit that target in 2015: the U.S., Britain, Greece, Poland and Estonia.

He said defense outlays in 18 other NATO countries are forecast to rise, but still the alliance-wide total is expected to drop in 2015.

This comes on top of a steady decline in defense expenditures, especially among NATO's European allies, during a long period of time, Stoltenberg told reporters. He said he would raise the issue with alliance defense ministers when they meet in Brussels on Wednesday.

"We need to redouble our efforts to reverse this trend," the NATO chief said. "Because we are facing more challenges, and we cannot do more with less indefinitely."

The ministerial meeting will be attended by U.S. Defense Secretary Ash Carter and counterparts from across the 28-nation alliance. They are expected to take several decisions designed to make NATO more nimble and responsive to the new security realities created by Russia and the Muslim extremism that has taken root in large swaths of the Middle East and North Africa.

Among the items to be decided by the ministers are the air, sea and special forces components for NATO's new rapid-response force, Stoltenberg said. Defense ministers will also be asked to approve a revamp of NATO's political and military decision-making process to allow quicker deployment of the force, he said. They are also expected to grant the alliance's supreme commander in Europe, Gen. Philip Breedlove, "more authority to prepare our troops for deployment and get them ready to go."