Poland's Foreign Minister Jacek Czaputowicz said on Wednesday that only the United States can guarantee the security of the eastern flank of NATO and that transatlantic unity must be maintained. Czaputowicz's remarks came ahead of the two-day NATO summit, which was set to begin later on Wednesday. The Polish foreign minister was speaking at a panel discussion with German Defence Minister Ursula von der Leyen and Turkey's top diplomat Mevlut Cavusoglu. Czaputowicz noted that the military alliance is undergoing transformation to adjust to new dangers, but they are perceived differently in Poland, the Baltic States or Georgia, which is not a NATO member. For central and eastern Europe, he said, the main threat is "the aggressive policy of Russia".