The Trump administration plans to inform NATO allies this week that it will reduce the U.S. military resources available to support European nations in a major crisis, according to three sources familiar with the matter.

Under a framework known as the NATO Force Model, the alliance's member countries identify a pool of available forces that could ​be activated during a conflict or any other major crisis, such as a ​military ⁠attack on a NATO member.

While the precise composition of those wartime forces is a closely guarded secret, the Pentagon has decided to significantly scale down its commitment, said the sources, who requested anonymity to speak candidly about the plans.

U.S. President Donald Trump has made clear he expects European countries to take over primary responsibility for the continent's security from the United States. The message to allies this week is a concrete sign of that policy being implemented.

Several details were unclear, such as how quickly the Pentagon plans to shift crisis-mode responsibilities onto European allies. The sources said, however, that the Pentagon plans to announce its intention to lessen its commitment at a Friday meeting of defense policy chiefs in Brussels.