By Andrius Sytas
VILNIUS (Reuters) -Estonian Prime Minister Kaja Kallas submitted her resignation on Monday in order to take up a new job as the European Union's foreign policy chief, the president's office said.
Kallas, 47, has emerged as a strong critic of neighbouring Russia and what she says are its expansionist aims since she became prime minister in early 2021. She has pressed Estonia's allies in NATO and the EU to provide unconditional support for Ukraine in its struggle to push back Moscow's invading forces.
Under her leadership, Estonia, a small Baltic republic of 1.4 million people, has become one of the biggest donors of military aid to Ukraine on a per capita basis.
Kallas led her liberal Reform party to victory in parliamentary elections in 2019 and 2023 and has fronted the government since 2021.
The Reform party has tapped Climate Minister Kristen Michal to become Estonia's next prime minister, pending negotiations to reconfigure the cabinet with its coalition partners, the liberal Estonia 200 and the Social Democrats.
Kallas will remain as Estonia's caretaker prime minister until the next government is confirmed by early August, Estonia's public broadcaster ERR said.
Her party will elect its new leader on September 8.
(Reporting by Andrius Sytas in VilniusEditing by Essi Lehto, Louise Rasmussen, Sharon Singleton and Gareth Jones)