One of the nation’s most respected foreign policy experts who once served as the United States Ambassador to Greece— and many believe is a top contender to be Joe Biden’s Secretary of State should he win in November— Tweeted that the U.S. needs to stand firmly in support of Greece.

Nicholas Burns, one of the top statesmen in America’s foreign policy establishment, having served in the country’s top diplomatic posts and in senior positions for both Republican and Democratic administrations, said in a Tweet that “Diplomacy is the key in reducing tensions between #Greece and Turkey in the Eastern Mediterranean. Important that the U.S. stand behind Greece and warn Turkey to stand down in its aggression.”

Burns, 63, is a professor at the Kennedy School of Government at Harvard University, Executive Director of the Aspen Strategy Group and served as the Under Secretary of State for Political Affairs under George W. Bush’s administration.

A member of the Biden campaign as a foreign policy advisor, Burns’ name has come up in public and private circles as a leading candidate to become America’s top diplomat at a time when relations with allies are strained and many career diplomats claim the department needs institutional revamping.

He served for five years on the National Security Council under Presidents George H.W. Bush and Bill Clinton. Under George W. Bush, he was US ambassador to NATO and later the third-highest ranking State Department official— the Under Secretary of State— before retiring from public service in 2008.

Burns was one of the earliest supporters of Joe Biden’s campaign and has been an outspoken critic of President Donald Trump’s foreign policy, at the same time helping Biden’s foreign policy team draft a slate of positions for a potential Biden Administration.

Over the past two months Burns has been active on foreign policy issues directly related to Greece and Cyprus, as well as the Greek American community. He moderated a discussion with Prime Minister Kyriakos Mitsotakis for the Aspen Security Forum and then headlined a kickoff event for Greek Americans for Biden.