BRUSSELS—A military unit that is on permanent high alert and can move rapidly when a crisis arises will be approved by the leaders of North Atlantic Treaty Organization when they meet in Wales this week, the secretary-general of the alliance said on Monday.

"This force can travel light, but strike hard if needed," Anders Fogh Rasmussen told reporters. This would be a "very high-readiness force able to deploy at very short notice," he added.

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