IN POLAND, NEAR THE UKRAINIAN BORDER — In a risky and secret visit to Ukraine, the United States’ top diplomat and defense officials arrived in Kyiv on Sunday, with announcements of sweeping diplomatic changes and new military aid for the embattled country.
Secretary of State Antony J. Blinken and Defense Secretary Lloyd J. Austin III met with President Volodymyr Zelensky, following other world leaders who have visited the capital over two months of war to signal their support for Ukraine.
In a move of symbolic and practical significance, the delegation told the Ukrainian president that the United States would move to reopen its embassy in Kyiv, and for the first time since 2019, nominate an American official to lead it.
President Biden is set to announce the nomination of Bridget Brink, the current US ambassador to Slovakia, as ambassador to Ukraine in Washington on Monday morning, according to a senior State Department official.
The coming changes were announced in a briefing to reporters in Poland by a senior State Department official and a senior defense official who were not authorized to speak publicly about coming policy changes.
American diplomats will begin crossing the border into Ukraine this week, the State official said, and will reopen the Kyiv embassy as soon as feasible to begin re-establishing contacts throughout the country in person.
Mr. Blinken’s and Mr. Austin’s trip had been planned in extraordinary secrecy, with only a small portion of their staff aware of their intent to visit Mr. Zelensky in Kyiv and even fewer allowed to travel with them. The trip remained under wraps until it was well underway, with both cabinet secretaries flying in nondescript Air Force cargo planes that were about halfway to Poland when the Ukrainian president unexpectedly announced the US visit in a news conference on Saturday.
In the latest of a series of increasing military aid announcements, Mr. Biden is expected to commit $713 million in new military financing for Ukraine and 15 other nations in Eastern Europe, the State Department official said, raising the United States’ total military aid to Kyiv to $3.7 billion since Feb. 24.
The funding is intended to assist the Ukrainians in the fight for the Donbas region by allowing Ukraine’s troops to transition to more advanced weapons and air-defense systems, the officials said. The assistance will also go toward funding ordnance used by Soviet-designed weapons like rockets, assault rifles and machine guns still used by the Ukrainian army.
The Biden administration has backed Ukraine with aid and weaponry, and has helped lead an international campaign of sanctions against Russia. But it had been under growing pressure to send a high-level official to Kyiv after recent visits there by several European officials, including Prime Minister Boris Johnson of Britain, who walked the streets with Mr. Zelensky, and the prime ministers of Spain and Denmark .
US officials purposefully did not announce the visit ahead of time, but Mr. Zelensky revealed Mr. Blinken and Mr. Austin would come to Kyiv in a news briefing on Saturday, saying he would use the meeting to discuss “the military assistance we need. ” The Pentagon and State Department did not immediately comment as it pressed ahead with getting the cabinet secretaries in and out of the country as safely and quietly as possible.
Mr. Blinken was the last high-ranking US official to visit Ukraine when he stopped there in mid-January. The United States closed its embassy in Kyiv on Feb. 14 and its diplomats soon left the country.
Russia’s invasion began 10 days later, and as it tried to seize the capital in an initial offensive, parts of Kyiv were struck by shelling and Ukrainian and Russian forces fought in the streets of Kyiv’s suburbs. But Russia’s retreat from the area around Kyiv appears to have made the city far less dangerous than it was a few weeks ago, and Western leaders have been taking the opportunity to demonstrate solidarity with Mr. Zelensky.
In March, only a few weeks after Russia’s invasion, the prime ministers of Poland, the Czech Republic and Slovenia traveled to Kyiv on a mission that was kept tightly under wraps. Over the following weeks, they were followed by leaders of Britain, Lithuania, Latvia, Slovakia, Estonia, Spain and Denmark. Ursula von der Leyen, the president of the European Commission, visited both Kyiv and Bucha, where, in the wake of Russia’s retreat, journalists and investigators have found evidence of atrocities.
In March, Vice President Kamala Harris traveled to Poland, where she expressed American support for Ukraine and US allies in NATO and the European Union. Mr. Blinken went as far as Poland’s border with Ukraine, meeting with Ukrainian diplomats at a crossing used by hundreds of refugees over the course of an hour.
President Biden also visited a town near the border on a state visit to Poland on March 25, but he did not cross into Ukraine. He met with refugees and gave a speech in Warsaw the next day.
Previous visits by senior American officials to other war zones, such as Iraq and Afghanistan, were typically not announced until after the official had arrived in the country — and sometimes not even until after they had left.
Security concerns and contested airspace have still required leaders to make long journeys to reach Kyiv. The British government said that Mr. Johnson, whose visit in early April was unannounced, used several modes of transportation, including a train from eastern Poland.
The White House had ruled out sending Mr. Biden, citing not only the risk but Mr. Biden’s enormous security requirements. Senior cabinet officials such as Mr. Blinken and Mr. Austin travel with smaller entourages.
John Ismay reported from an undisclosed location in Poland near the Ukrainian border; Eduardo Medina from New York; and Michael Crowley from Washington.