KIEV, Ukraine — Senior Ukrainian officials said they were blindsided over the summer when they heard the United States would withhold security assistance to the country.
“It was a total surprise,” said Pavlo A. Klimkin, who was Ukraine’s foreign minister in August when he learned of the Trump administration’s suspension of military aid by reading a news article.
The blocking of military aid to Ukraine is now at the center of questions about whether President Trump manipulated foreign policy to pressure the Ukrainian government to take action that would hurt Joseph R. Biden Jr., the former vice president and a top rival in the campaign for the presidency.
President Trump acknowledged on Sunday that he used a July 25 phone call with the new Ukrainian president, Volodymyr Zelensky, to accuse Mr. Biden of corruption.
Mr. Biden oversaw American policy toward Ukraine in the Obama administration when his son served on the board of a Ukrainian natural gas company. Allies of Mr. Trump have pointed to a conflict of interest, and asked Ukraine to investigate Mr. Biden’s request in 2016 that Ukraine’s president at the time, Petro O. Poroshenko, dismiss a prosecutor who had investigated the gas company.
By the time of that July 25 call, the administration had already suspended the aid, a decision reached in early July, according to a former American official.
But the news would not reach the Ukranian officials until much later, and then through nonofficial channels. For years, Ukranian officials had coordinated with the Pentagon, the State Department and members of Congress on military aid.
Mr. Klimkin said he received no formal notice through American diplomatic channels of the halt in aid, although he noted the suspension came as the ministry was transitioning to a new administration. He left the ministry on Aug. 29.
American military assistance for Ukraine had flowed unobstructed into the country since 2014, the year Russia annexed Crimea and fomented a war in two eastern provinces. The aid had always arrived in carefully choreographed shipments planned months in advance.
If the United States harbored concerns about any misuse of the aid by Ukraine, the senior officials said they had never heard about them.
Mr. Klimkin said American officials had always provided the aid along with encouragement to overhaul the army and military industries to root out corruption.
But Mr. Klimkin said that aid was not conditional on those issues, and that he had heard no expressions of concern on those fronts from the United States in 2019.
“I never heard a discussion about meeting these conditions,” he said. “I’m not aware of any indication that something could have gone wrong.”
After a bipartisan outcry in Congress, the White House agreed to restore the aid in mid-September.
If the decision to suspend the aid was tied to a request by Mr. Trump for a politically motivated investigation, that “represents a fundamental challenge and problem for Ukraine,” Mr. Klimkin said, possibly threatening what had been bipartisan support in Congress for military assistance to the country.
“At the end of the day, the only ones who will be happy about that are the people sitting in the Kremlin,” he said.
In an interview on Ukrainian television on Saturday, Ukraine’s current foreign minister, Vadym V. Prystaiko, said Mr. Trump had not pressured Mr. Zelensky in the telephone call.
“There was talk, conversations are different, leaders have the right to discuss any problems that exist,” he said. “This conversation was long, friendly, and it touched on a lot of questions, including those requiring serious answers.”
Another official who learned of the hold on aid like a bolt from the blue was Oleh Shevchuk, who was deputy minister of defense in charge of logistics and oversaw the aid shipments until this month. He also said he learned of it through media reports.
Everything had been arriving smoothly, he said. Even as the news of the suspension came out, he said, Ukraine was receiving containers of medical supplies in Odessa, a Black Sea port. The Ukrainian military was expecting 33 Humvees equipped as ambulances, water purifying equipment and so-called containerized housing units, or mobile homes for soldiers. The Ukrainian military still expects these items, he said.
In fact, the hold came and went so quickly he noticed no change in the shipments and American officials never informed him of any planned delays, Mr. Shevchuk said. “We got more this year than last year,” he said.
The United States has provided about $1.5 billion worth of military aid to Ukraine since 2014, almost entirely as equipment, often drawn from United States Army surpluses, rather than money transfers to the Ukrainian budget.
It includes items much sought-after on the battle front, like body armor, night-vision goggles and armored ambulances. But the aid has not been decisive in the now five-year-old war. Some aid, including ready-to-eat meals and at least one sophisticated counter-battery radar, has been captured and gleefully put on display by the Russian-backed separatists.
As a major component of the aid, about 300 American soldiers serve as trainers at a military base in western Ukraine, far from the fighting in the east.
Oksana Syroid, a former deputy speaker of the Ukrainian Parliament, said in an interview that no American concerns about military aid crossed her desk this year before the hold was announced.
“It’s a very slippery road, a very dangerous approach, to make external relations a hostage to internal politics,” she said of a possible tie of the aid to corruption accusations against Mr. Biden. “It’s like asking a neighbor to take sides in an argument with your spouse.”