A few months ago, Oleh Voroshylovskyi, the commander of a Ukrainian unit tasked with shooting down Russian drones attacking Kyiv, received a coveted American weapon to aid in their mission — a Browning machine gun capable of firing rounds at targets over a mile away.

Not only would it help the unit target Russian drones at higher altitudes, it also symbolized, at the unit’s level, America’s support for Ukraine in the war against Russia.

But after the Trump administration announced on Tuesday a pause in the delivery of some air defense interceptors and other weapons to Ukraine, because of what it said were dwindling U.S. stockpiles, Mr. Voroshylovskyi is no longer sure about America’s continued support.

“This will have a serious impact on combat effectiveness,” he said in a telephone interview on Wednesday.

The deliveries now on hold were all allocated under the Biden administration, and Mr. Trump has not approved new military aid packages for Ukraine. Washington had committed to delivering as much as $11 billion in weapons and equipment to Ukraine this year.

Among the munitions now being withheld are missiles for U.S.-designed Patriot air defense systems, precision artillery rounds and other missiles that Ukraine fires from its American-made F-16 fighter jets. Although it is unclear how many weapons were included, the signal seems clear: Washington is disengaging from the war.

“Ukraine is no longer a priority, no longer at the center of the U.S. foreign policy,” Solomiia Bobrovska, a member of the Ukrainian defense and intelligence parliamentary committee, said in a telephone interview. “At least Trump is very honest about this with the Ukrainians.”

Ukrainian officials appeared caught off guard by the announcement. The defense ministry said that it had not received any official notification about the suspension, and that it had “requested a phone conversation with U.S. counterparts to further clarify the details.”

It is unclear how deeply the pause will affect Ukraine, which is now getting weapons from Europe and making its own.

It is a particularly precarious time for Ukraine, because Russia is pounding the country every few days with large-scale air assaults intended to break its air defenses. Moscow now regularly sends hundreds of drones in a single night followed by powerful ballistic missiles that only Patriot missiles can intercept.

In a sign of its concern, Ukraine summoned the U.S. Embassy in Kyiv’s deputy chief of mission, John Ginkel, on Wednesday to discuss “U.S. military assistance and defense cooperation.”

“The Ukrainian side emphasized that any delay or slowing down in supporting Ukraine’s defense capabilities would only encourage the aggressor to continue war and terror, rather than seek peace,” Ukraine’s foreign ministry said in a statement.

Several Ukrainian lawmakers also voiced dismay over the White House’s decision, warning that it would only enable the Kremlin to inflict even greater destruction on Ukraine. “Hundreds of deaths from civilian targets will be on the conscience not only of Putin, but also of Trump,” Inna Sovsun, an opposition lawmaker, wrote on X.

This is the second pause since President Trump returned to office. In March, the White House briefly halted all military aid to Ukraine after a tense meeting between Mr. Trump and President Volodymyr Zelensky.

Since then, signs of the Trump administration’s disengagement have multiplied, from echoing Kremlin talking points to pushing Ukraine down the list of priorities at last week’s NATO summit in The Hague.

On Wednesday, the Kremlin lauded Washington’s halt in weapons supplies to Ukraine and argued that the move could help bring about an end to the fighting.

“As far as we understand, this decision is due to empty warehouses: low stockpiles of weapons at the warehouses,” Dmitry S. Peskov, the Kremlin spokesman, told Russian news agencies. “But in any case, the less weaponry gets sent to Ukraine, the sooner the end of the special military operation is,” he said, using Russia’s official term for the war.

Ukraine has eight Patriot systems, six of which are operational, largely to protect Kyiv, the capital, a prime target of Russian attacks. But ammunition is running low and the pause will make it significantly harder to protect the city, Ms. Bobrovska said.

“That’s a huge problem,” she said.

She said the pause in other weapons deliveries, such as artillery rounds, would be easier to manage, given that Ukraine is increasing domestic production and receiving more supplies from its European partners. Mr. Zelensky said last week that Ukraine’s defense industry was now providing more than 40 percent of the weapons the country is using in the war.

After the United States halted all weapons deliveries to Ukraine in March, analysts estimated that Ukraine could keep up the fight for four to six months. The Trump administration lifted that pause after about a week, and arms shipments resumed.

Calculating that the Trump administration is unlikely to pledge any further military aid, Kyiv has shifted to another strategy, saying that it was ready to purchase American weapons rather than receive them as donations. Mr. Zelensky said in April that he was ready to buy 10 Patriot systems for about $15 billion.

At last week’s NATO summit, Mr. Trump suggested that he was open to sending more Patriots to Ukraine, though it was unclear whether he meant batteries or only ammunition, and whether they would be donated or sold.

To compensate for the drop in U.S. weapons deliveries, Ukraine has recently launched joint arms production programs with European allies like Britain, Denmark, and Norway. Under that initiative, weapons will be manufactured in those countries or in Ukraine, with allies providing the funding and Ukraine contributing technical expertise.

Mr. Voroshylovskyi, the commander of the anti-drone unit near Kyiv, insisted that Ukraine could endure the latest pause in U.S. deliveries — though at a steep cost.

“We’ll find weapons,” he said. “It will be harder. Many more people will die.”

Daria Mitiuk and Nataliia Novosolova contributed reporting from Kyiv, and Nataliya Vasilyeva from Istanbul.