By Gram Slattery and Angelo Amante ANKARA/ROME, July 7 (Reuters) - U.S. President Donald Trump on Tuesday called Italian Prime Minister Giorgia Meloni a "nice person" but criticised her for failing to help in the conflict with Iran, his latest remarks in a diplomatic dispute that is straining bilateral ties. Meloni was once seen as a close ally of Trump, but the relationship faltered last month when he told Italian TV channel La7 that she had "begged" him to take a photo with her at a G7 summit