By Timothy Gardner and Kate Abnett WASHINGTON/BRUSSELS (Reuters) -The United States and the European Union pledged on Monday to work to ensure gas supplies can respond to disruptions in pipeline gas flows, as tensions rise over the massing of troops on Ukraine’s borders by Russia, Europe’s biggest gas supplier. “We’re working together right now to protect Europe’s energy supply against supply shocks, including those that could result from further Russian aggression against Ukraine,” U.S. Secretary of State Antony Blinken told reporters in Washington, alongside Josep Borrell, the EU foreign pol…