BRUSSELS (Reuters) - NATO allies on Wednesday selected Dutch Prime Minister Mark Rutte as NATO's next boss, as the war in Ukraine rages on its doorstep and uncertainty hangs over the United States' future attitude to the transatlantic alliance.

Rutte's appointment became a formality after his only rival for the post, Romanian President Klaus Iohannis, announced last week that he had quit the race, having failed to gain traction.

(Reporting by Andrew Gray; Editing by Sudip Kar-Gupta)