WARSAW, March 27 (Reuters) - Poland has detained a foreign citizen on charges of spying for Russia, prosecutors said on Monday, as the largest country on NATO's eastern flank finds itself increasingly targeted by Moscow's intelligence services. The war in Ukraine has plunged what were already strained relations between Poland and Russia to new lows, with Warsaw saying it is frequently the subject of Russian espionage and disinformation. See here for a complete list of exchanges and delays