The Pentagon is building a missile-defense radar station at a secret site in Qatar and organizing its biggest-ever minesweeping exercises in the Persian Gulf, as preparations accelerate for a possible flare-up with Iran, according to U.S. officials. The radar site will complete the backbone of a system designed to defend U.S. interests and allies such as Israel and European nations against Iranian rockets, officials told The Wall Street Journal. The minesweeping exercises, in September, will be the first such multilateral drills in the region, and are expected to be announced by U.S. officials Tuesday.