Secretary of State Antony J. Blinken suggested on Wednesday that the Biden administration could be open to tolerating strikes by the Ukrainian military inside Russia using American-made weapons, saying that the United States would “adapt and adjust” its stance based on changing conditions on the battlefield.

Mr. Blinken said that the United States had neither encouraged nor enabled such attacks. But he said that the Ukrainians needed to make their own decisions on how to best defend themselves — a position he has stated before — and that the U.S. government had “adapted and adjusted as necessary” as the war evolves.

When asked by a reporter whether his words “adapt and adjust” meant the United States could support attacks by Ukraine with American-made weapons inside Russia, he said, “Adapt and adjust means exactly that” — meaning those words, signaling flexibility from Washington.

Since Russia launched its full-scale invasion of Ukraine in February 2022, Washington has sent the Ukrainians military aid but has repeatedly asked that they not fire U.S.-made weapons into Russian territory for fear of escalating the war.

Several European leaders have called on President Biden to stop imposing those limits, among them Jens Stoltenberg, the secretary general of the North Atlantic Treaty Organization, and Emmanuel Macron, the president of France.

Mr. Blinken made his remarks in Chisinau, the capital of Moldova, while standing beside Maia Sandu, the nation’s president, who is expected to face a pro-Russian candidate when she runs for re-election in October. The two spoke to journalists after an afternoon meeting in the presidential offices.

“Our neighbors, our friends in Ukraine, they pay an outrageous price on a daily basis,” Ms. Sandu said.

Mr. Blinken announced new aid to Moldova to address a range of issues arising from Russian aggression, including its invasion of Ukraine.

The first of two packages mentioned was $50 million in broad support for Moldova’s industry and government, as well as for democratic processes. Mr. Blinken mentioned the energy and agriculture sectors, and the need to combat disinformation.

“What’s so powerful here is the deep and deep-rooted commitment to democracy,” Mr. Blinken said, “in the face of bullying from Russia.”

Ms. Sandu thanked Mr. Blinken for American help in fighting corruption, building renewable-energy infrastructure and addressing the “adversities of democracy,” a nod to Russian election interference.

The second aid package mentioned was $85 million to help Moldova increase its energy resiliency and reduce its dependence on electricity generated in a Russian-backed separatist region in the east, Transnistria. These funds, part of a $300 million commitment previously announced by the United States Agency for International Development, would help Moldova strengthen its battery storage capabilities and high-voltage transmission lines, among other energy needs, Mr. Blinken said.

Moldova recently ended its reliance on natural gas imports from Russia and now buys gas from a number of countries, including the United States.

Mr. Blinken’s visit to Chisinau was the first stop in a trip aimed at showing U.S. support for nations facing a hostile Russia. Mr. Blinken is going next to the Czech Republic, where he is scheduled to attend a meeting of foreign ministers and top officials of NATO on Thursday and Friday. They plan to discuss how to best support Ukraine.

This trip follows Mr. Blinken’s overnight visit to Kyiv more than two weeks ago.

Ms. Sandu has advocated Moldova’s entry into the European Union, and has scheduled a referendum on the question for the same day as the presidential election in October.

U.S. and European analysts say Moscow is likely to try to interfere in the election, as it has done elsewhere in Europe. The Biden administration has spoken publicly of Russian agents carrying out such interference using different means, from hacking to orchestrating campaigns over social networks to doling out money to favored politicians.

About 1,500 Russian troops are in Transnistria, which borders Ukraine. U.S. officials are watching for any signs that President Vladimir V. Putin of Russia might try to annex the territory.

The NATO session in the Czech Republic is officially aimed at firming up the agenda for a meeting of alliance leaders in Washington in July. The group is not expected to declare that Ukraine will now join NATO, an aspiration that Mr. Zelensky has reiterated following the Russian invasion. They are, however, expected to work out details for moving Ukraine along the process of joining.

As Russian troops press an offensive in Ukraine’s second-largest city, Kharkiv, the Ukrainian war effort has been flagging, in large part because of a shortage of weapons and munitions. There are also fewer citizens able to join the fight.

Mr. Biden recently signed a bill passed by Congress, despite some Republican opposition, that grants new military aid to Ukraine.

Russia is producing munitions at a rapid rate, and U.S.-led sanctions have failed to cripple its military industrial capabilities. Mr. Biden and his aides say China has played a decisive role in bolstering Russia through exports of dual-use equipment and other goods that have allowed it to strengthen weapons production. Mr. Blinken is expected to highlight China’s support for Russia in his discussions at the NATO meeting in Prague.