A State Department spokesperson said in a statement on May 6 that Ambassador Marie Yovanovitch "is concluding her 3-year diplomatic assignment in Kyiv in 2019 as planned."
"Her confirmed departure date in May aligns with the presidential transition in Ukraine," which elected a new president last month, the spokesperson said.
"The team at U.S. Embassy Kyiv, and in Washington, continues to work closely with the Ukrainian government and civil society to strengthen our partnership," the spokesperson added.
The statement did not provide further details.
Sworn in as ambassador to Kyiv in August 2016, Yovanovitch has been at the forefront of the US efforts to help stabilize Ukraine's shaky economy and push reforms to root out endemic corruption.
She's also been at the forefront of the S backing for Ukraine in its ongoing fight with Moscow over Russia-backed fighters battling Ukrainian government forces in eastern regions since 2014.