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The US has reopened its embassy in Ukraine's capital Kyiv on Wednesday, US Secretary of State Antony Blinken said.
It marks a major move in American support for President Volodymyr Zelenskyy's government after nearly three months of Russia's invasion, which started on February 24.
"The Stars and Stripes fly again over embassy Kyiv," Mr Blinken tweeted, along with photos of the building.
"I can announce that we have officially resumed embassy operations in Ukraine’s capital."
"We stand proudly with the government and people of Ukraine as they bravely defend their country from Putin’s brutal invasion. Slava Ukraini," he said, which means "Glory to Ukraine".
Kyiv still faces air attacks from Russia and Mr Blinken is aware of that.
"We are committed to confronting the challenges ahead," he said. "The war rages on. Russia’s forces inflict death and destruction on Ukrainian soil every day.
"With strength of purpose, we reaffirm our commitment to the people and government of Ukraine, and we look forward to carrying out our mission from the US embassy in Kyiv."
The US had closed its embassy and withdrew its staff in Kyiv on February 12 before the Russian invasion.
State Department personnel were relocated to the western city of Lviv, while other staff were sent to Poland.
"As we take this momentous step, we have put forward additional measures to increase the safety of our colleagues who are returning to Kyiv and have enhanced our security measures and protocols," Mr Blinken said.
Top US officials, including Mr Blinken and Secretary of Defence Lloyd Austin, have met Mr Zelenskyy, and other American politicians have visited Kyiv on visits over the past month.
US President Joe Biden's wife Jill visited last week to meet Mr Zelenskyy's wife Olena Zelenska.
Other countries including Britain have reopened their embassies in Kyiv recently.