KYIV, Ukraine (AP) — U.S. Secretary of State Antony Blinken met with top Ukrainian officials in Kyiv Thursday and reaffirmed Washington's support for the country in the wake of heightened tensions with Russia, fueled by its recent troop buildup near the borders with Ukraine.

The top American diplomat met with Ukrainian President Volodymyr Zelenskyy and reiterated the U.S.'s commitment to Ukraine's “sovereignty, territorial integrity and independence,” while also underscoring the importance of Ukraine's efforts to tackle widespread corruption and carry out reforms.

“Ukraine is facing two challenges: aggression from outside, coming from Russia, and in effect aggression from within, coming from corruption, oligarchs and others who are putting their interests ahead of those of the Ukrainian people,” Blinken told a news conference after his meeting with Zelenskyy.

By visiting so early in his tenure, before any trip to Russia, Blinken signaled that Ukraine is a high foreign-policy priority for President Joe Biden’s administration. His visit was highly anticipated in Ukraine, with hopes for increased military aid and strong support for NATO membership being voiced on the frontlines of the battle against Russia-backed separatists in the east and in the halls of government in Kyiv.

Ukraine has seen an increase in hostilities in the east in recent months. Ukraine’s military says 34 of its soldiers have been killed by rebel attacks this year, a significant upswing from the quiet months of the latter part of 2020. Russia, which claims its soldiers are not on the ground in eastern Ukraine, fueled the tensions further this year by massing troops and conducting large-scale military exercises near the border with Ukraine.

Zelenskyy has made it clear that he wants significant action — “a clear signal about the European and Euro-Atlantic prospect,” as he said on Twitter on Monday, referring to Ukraine's aspirations to join NATO and the European Union. “Postponing these issues for ‘later,’ ‘some day,’ ‘(in) 10 years’ has to end.”

Blinken reiterated Washington's commitment to Ukraine's “independence, to its sovereignty, to its territorial integrity” at the news conference Thursday. He said that Ukraine's “Euro-Atlantic aspirations” were discussed during his meeting with Zelenskyy and that the U.S. was “actively looking” at strengthening its security assistance to Ukraine, but didn't offer any details.

Zelenskyy also said that the military support and the financial support from the U.S. “is increasing,” but didn't elaborate.

Both noted that while Russia has pulled back some of its forces from the borders, a significant amount of troops and equipment still remains there. Blinken said Washington was watching the situation “very, very closely," as “Russia has the capacity, on fairly short notice, to take aggressive action if it so chooses."

“I can tell you, Mr President, that we stand strongly with you," Blinken said.

In Brussels on Thursday, NATO Secretary General Jens Stoltenberg also said the 30-nation military alliance “needs to stay vigilant and closely monitor the developments” in and around Ukraine. “We have seen some reduction in the number of Russian troops, but tens of thousands remain, and we also see that Russia has kept a lot of weapons, prepositioned equipment, and they’re also imposing restrictions in the Black Sea,” Stoltenberg told reporters.

Efforts have stalled to end the conflict in eastern Ukraine, which has killed more than 14,000 people since it broke out in 2014. Zelenskyy has called for the United States to try to push these efforts forward by joining the negotiations of the “Normandy Format” that consists of Russia, Ukraine, Germany and France. Russia is almost certain to oppose any U.S. involvement in the negotiations.

Earlier this week, Foreign Minister Dmytro Kuleba said Ukraine was also worried about Russia’s announcement last month that it was redeploying warships from its Caspian flotilla to the Sea of Azov, an extension of the Black Sea that borders Ukraine and Russia. “There is now a big threat in the Sea of Azov; it is unprecedentedly large,” Kuleba said.

Zelenskyy said Thursday that he discussed the issues of security in the Black Sea and the Sea of Azov with Blinken, but wouldn’t reveal any details.

Ukraine's leader also said he invited Biden to visit Ukraine this year, and Blinken said the U.S. president would “welcome the opportunity at the right time.”

Earlier in the day, Blinken met with Kuleba, and they both joined Metropolitan Epiphaniy — head of the Ukrainian Orthodox Church, which split from Russia’s Orthodox Church. They laid flowers at a memorial to Ukrainian soldiers killed in the conflict in the east of the country and toured St. Michael’s Monastery.

Blinken also met with Prime Minister Denys Shmyhal, who said on Twitter that his visit to Kyiv was “a manifestation of firm support and a high level of relations of two states.”

Analyst Volodymir Fesenko of the Penta Center said Ukraine is expecting "the expansion and strengthening of U.S. assistance to Ukraine to successfully repel Russian aggression.”

“Ukraine wants not only to receive encouraging political signals, but wants the United States to take a clear and very tough position on the further integration of Ukraine into NATO, so that the United States acts not just as a lawyer for Kyiv, but as an insisting party,” Fesenko said.