U.S. Secretary of State Antony Blinken announced Wednesday that the U.S. is officially resuming operations at its embassy in Kyiv.

"The Ukrainian people, with our security assistance, have defended their homeland in the face of Russia’s unconscionable invasion, and, as a result, the Stars and Stripes are flying over the Embassy once again," Blinken said in a statement.

The U.S. has put in place additional measures to increase the safety for its staff and enhanced its security measures and protocols.

"We are committed to confronting the challenges ahead," Blinken said. "We reaffirm our commitment to the people and government of Ukraine, and we look forward to carrying out our mission from the U.S. Embassy in Kyiv."

Finland and Sweden formally submitted their applications to join NATO to Secretary General Jens Stoltenberg Wednesday morning at the alliance’s Brussels headquarters.

Stoltenberg welcomed the requests, saying, "This is a good day, at a critical moment for our security," according to NATO.

"Every nation has the right to choose its own path. You have both made your choice, after thorough democratic processes. And I warmly welcome the requests by Finland and Sweden to join NATO," Stoltenberg said Wednesday.

Adding, "You are our closest partners. And your membership in NATO would increase our shared security."

Russian Sgt. Vadim Shyshimarin pleaded guilty Wednesday to shooting a 62-year-old Ukrainian man on Feb. 28. The guilty plea carries a life sentence.

It's the first trial Ukraine has conducted for an act that could be considered a war crime.

Asked by the presiding judge whether he accepted his guilt, Shyshimarin said: "Yes. Fully yes."

Kremlin spokesman Dmitri Peskov dismissed the proceedings on Wednesday, telling reporters that accusations leveled against Russian soldiers by Ukraine were "simply fake or staged."

-ABC News' Joe Simonetti

As Turkey becomes more vocal about its opposition to Sweden and Finland joining NATO, the State Department said it is still assured of the alliance's unified support for the two prospective members.

State Department spokesperson Ned Price said during a briefing Tuesday that Secretary of State Antony Blinken came away from meetings with NATO allies with a "sense of confidence there was strong consensus for admitting Finland and Sweden into the alliance if they so choose to join, and we're confident we'll be able to preserve that consensus."

Price said that assessment came from what Blinken heard in conversations behind closed doors.

Turkey's president, Recep Tayyip Erdogan, has publicly said that both candidates are untrustworthy because he perceives them as being supportive of groups Ankara views as extremist.

There is speculation that Turkey’s opposition is an attempt to leverage the moment to achieve its own policy goals or concessions from the U.S. Price said Tuesday that Turkey has not made any specific requests.

Price confirmed that Blinken will meet with his Turkish counterpart on the sidelines of the U.N. on Wednesday, adding that "other conversations are ongoing between and among current NATO allies and potential aspirant countries."

-ABC News' Shannon Crawford

Mariupol has not yet fallen, despite Russia's demands that Ukrainian troops defending the besieged Ukrainian port city surrender, according to Ukrainian Prime Minister Denys Shmyhal.

"There [are] still our military forces, our soldiers, so they will fight until the end," Shmyhal told ABC News' George Stephanopoulos in an exclusive interview Sunday on "This Week."

Mariupol is a strategic city for Moscow because it would allow Russian forces in the south to connect with troops in eastern Ukraine's contested Donbas region. It would also give Moscow a key port.

Although Mariupol remains under the Ukrainian government's control, Shmyhal said the city's residents are suffering.

"They have no water, no food, no heat, no electricity," he said. "They ask all of our partners to support and help stop this humanitarian catastrophe."

-ABC News' Monica Dunn