NATO head Jens Stoltenberg said Monday the alliance will approve plans this week to more than double the size of its rapid response force, having already created a special spearhead unit in the fallout from the Ukraine crisis.

"NATO defence ministers ... (will) take a decision to further increase the strength and capacity of the NATO Response Force to 30,000 to 40,000 troops, more than double its current size," Stoltenberg said ahead of a meeting Wednesday and Thursday in Brussels.