BRUSSELS - NATO this week is holding its biggest war game in years, and the Russians aren't happy it's happening so near their borders.

NATO Secretary General Anders Fogh Rasmussen said the exercise, codenamed Steadfast Jazz, was underway Monday, with 13 warships in the Baltic waters off Poland and dozens of planes in the skies of central Europe.

Steadfast Jazz will involve about 6,000 personnel from NATO member nations and partner countries. Rasmussen says it is meant to test the ability of NATO's multinational rapid-reaction Response Force to "deploy anywhere and deal with any threat."

Moscow has voiced displeasure the war game is being held in Poland and the former Soviet Baltic republics. Rasmussen says NATO has invited Russian observers to come see that the exercise is not "directed against Russia."