ANKARA, Turkey, July 7 (Reuters) - U.S. President Donald Trump said on Tuesday that Greenland should be controlled by the United States, not Denmark, as NATO leaders gathered for a summit in Turkey. Trump's assertions that the U.S. must acquire or control Greenland, a semi-autonomous Danish territory, sparked tensions between Washington and Copenhagen - both founding NATO members - and more broadly across Europe. The issue has since moved to a diplomatic track.