WASHINGTON, Sept 28 (Reuters) - U.S. Trade Representative Katherine Tai and her European Union counterpart discussed common challenges posed by non-market economies, including China, during a meeting in Washington on Tuesday, Tai"s office said in a statement. Tai thanked European Commission Executive Vice President Valdis Dombrovskis "for helping to build an important bilateral partnership and working constructively to strengthen the transatlantic trade and economic relationship." The statement made no mention of efforts to resolve a steel and aluminum tariff dispute between the United States and the EU. Reporting by David Lawder; editing by Jonathan Oatis Our Standards: The Thomson Reuters Trust Principles.