ATLANTA, June 20 (Reuters) - U.S. Treasury Secretary Janet Yellen on Thursday said the United States' upgraded partnership with Vietnam does not require Vietnam to sever ties with Russia or China.

Asked whether Russian President Vladimir Putin's visit to Vietnam to sign a slew of agreements ranging from oil and gas to nuclear science raised concerns for Washington, Yellen said Hanoi has a clear policy of working with many countries.

"Vietnam has a policy and strategy of working collaboratively with many different countries, and it is not a condition of our partnership that they sever their ties to Russia or to China," Yellen told a news conference in Atlanta. (Reporting by Rich McKay in Atlanta, writing by Andrea Shalal)