WASHINGTON—The U.S. government may expand coronavirus testing requirements for international air travelers beyond Britain as early as next week, sources briefed on the matter told Reuters Wednesday. The Centers for Disease Control and Prevention (CDC) and other U.S. agencies held a lengthy call with U.S. airlines Wednesday that discussed expanding COVID-19 test requirements to travelers arriving from other countries, sources briefed on the call said. The U.S. government on Monday began requiring all airline passengers arriving from Britain—including U.S. citizens—to test negative for COVID-19 within 72 hours of departure. The CDC said in a statement Wednesday that “efforts are currently ongoing in the U.S. to assess the risk reduction associated with testing and other recommended preventative measures, determine what a feasible testing regime for air travel may look like, and gain some level of agreement on standards for a harmonized approach to testing for international air travel.” A U.S. Transportation …