WASHINGTON, Jan 19 (Reuters) - The U.S. Treasury Department on Tuesday slapped sanctions on a vessel helping to build the Nord Stream 2 pipeline to take Russian natural gas to Europe via Germany. The department said it imposed the sanctions on the Russian pipe-laying ship “Fortuna” and its owner, KVT-RUS, under the Countering America’s Adversaries Through Sanctions Act (CAATSA). (Reporting by Timothy Gardner and Daphne Psaledakis)