Acting Assistant Secretary of State for East Asian and Pacific Affairs Susan Thornton attends a House Foreign Affairs Committee hearing on North Korea sanctions, Sept. 12, 2017,  in Washington.
Acting Assistant Secretary of State for East Asian and Pacific Affairs Susan Thornton attends a House Foreign Affairs Committee hearing on North Korea sanctions, Sept. 12, 2017, in Washington.

STATE DEPARTMENT - A senior U.S. diplomat for Asian affairs is leaving State Department at the end of July amid ongoing and critical negotiations with North Korea, weeks after the leaders of the U.S. and North Korea met in Singapore.

"Acting Assistant Secretary of State for East Asian and Pacific Affairs Susan Thornton has announced her intention to retire from the Foreign Service at the end of July," State Department spokeswoman Heather Nauert said Saturday in a statement.

"We particularly appreciate her dedication to department and interagency colleagues, her extraordinary leadership, especially as acting assistant secretary over the past year and a half," Nauert added.

Thornton was formally nominated by President Donald Trump as assistant secretary of state for East Asian and Pacific affairs last December. She began serving in the position in an acting capacity soon after Trump took office.

Thornton's nomination, which requires Senate confirmation, has been blocked by key Republicans, including Senator Marco Rubio of Florida.

In a tweet in May, Rubio said Thornton was "undermining" Trump's effort to negotiate with North Korea by suggesting that the U.S. might accept a "partial" surrender of its nuclear weapons at the start of the talks.

Rubio was quoting Thornton's remarks at a Wall Street Journal conference in Tokyo.

The State Department later clarified, saying Thornton's position was in line with that of Secretary of State Mike Pompeo. 

"What Susan Thornton was talking about is very similar and the same thing to what Secretary Pompeo spoke about, and that is that we would like to see a bigger, bolder, different, faster deal than the kind of deals that have been proposed before," Nauert said in a briefing May 17.

Pompeo is said to be working diligently on nominations to fill key leadership roles across the State Department, including the position of assistant secretary of state for East Asian and Pacific affairs.