President Joe Biden said Friday he will nominate Rahm Emanuel, who served as a top aide to former President Barack Obama, as U.S. ambassador to Japan, seeking to fill a key diplomatic post that has been vacant for about two years.

Biden also tapped Nicholas Burns, a former diplomat and currently a Harvard University professor, as U.S. ambassador to China.

The nominations will require Senate approval.

Rahm Emanuel. (Getty/Kyodo)

If confirmed, Emanuel, a 61-year-old former congressman known for his abrasive style and his close ties with Biden, formerly Obama's vice president, will be tasked with playing a key role in beefing up the bilateral alliance amid China's growing assertiveness.

Emanuel was White House chief of staff for Obama from 2009 to 2010 before becoming Chicago's mayor for two terms from 2011 to 2019. But he decided not to seek another term after facing criticism over the handling of a fatal shooting of a black teenager by a white police officer in 2014.

A delay in releasing video footage of the 17-year-old Laquan McDonald, who appeared in the video to be walking away from the police when he was shot 16 times, stirred criticism that Emanuel was involved in an alleged "cover-up" of the incident.

Left-wing Democrats and organizations have cited Emanuel's governing record to question whether he is qualified for the ambassadorship or any other high-profile role in the Biden administration, which places an emphasis on tackling racism.

"Emanuel's abysmal record as mayor of Chicago disqualifies him to represent the United States in a foreign capital," groups including the left-wing RootsAction said in a joint statement released in mid-March when some media reported the nomination plans.

In November last year, when speculation emerged about Emanuel's chances of landing a Cabinet post, House of Representatives member Alexandria Ocasio-Cortez, who is popular among young voters, said on Twitter, "Covering up a murder is disqualifying for public leadership."

The U.S. ambassadorship to Japan has been vacant since William Hagerty stepped down in July 2019 to run for the Senate.

Joseph Young, then deputy chief of mission at the U.S. Embassy in Tokyo, served as the interim charge d'affaires until June this year. Raymond Greene, formerly deputy director of the American Institute in Taiwan, Washington's de facto embassy, is currently serving as U.S. interim ambassador to Japan.

In March last year, Biden's predecessor Donald Trump nominated Kenneth Weinstein -- then head of the Washington-based conservative think tank the Hudson Institute -- as the next U.S. ambassador to Japan.

But Weinstein's nomination was not confirmed by the Senate. With Republican Trump defeated in the presidential election, Democrat Biden took office in January this year.

Burns, 65, was undersecretary of state for political affairs, the State Department's third-ranking official, from 2005 to 2008 under the George W. Bush administration.

He also served as U.S. ambassador to the North Atlantic Treaty Organization from 2001 to 2005.