WASHINGTON (Reuters) – The United States is in “constant contact” with Moscow about Brittney Griner, the U.S. WNBA basketball star being held in Russia, President Joe Biden said on Tuesday, after her appeal against a nine-year sentence for drug smuggling was denied. “We’re in constant contact with Russian authorities to get Brittany and others out. So far we’ve not been meeting with much positive response but we’re not stopping,” he said. Biden also warned Moscow against using a nuclear weapon, after Russia told the United Nations that it believed Ukraine was planning a “dirty bomb,” an allega…