Ukrainians have died because Kyiv is still not receiving reliable US warnings of incoming Russian attacks, according to a key adviser to President Volodymyr Zelensky.
Serhii "Flash" Beskrestnov told the BBC that lives had been lost because there had not been time to warn citizens about ballistic missile strikes, saying: "It's dangerous... I think it's really very bad... People [have] already died."
The adviser also said restrictions to Ukraine's use of the Starlink internet network were ongoing.
The White House said there had been no changes to intelligence sharing with Ukraine.
Ukraine first reported an interruption to US intelligence sharing last week, as a row with the Trump administrations over its controversial deal to import Russian oil sent relations to new lows.
Despite the denials from Washington, many in Kyiv suspect the issues are not a coincidence.
On Monday morning, Zelensky wrote on social media: "Overnight two ballistic missile attacks were reported on the capital, one without warning, the second with only minimal time to take shelter."
Hours earlier, an interview the president did with NBC was published, in which he said intelligence sharing had been restored after a three-day pause.
"We are very thankful for this," he said. "Only [the] United States has this unique intelligence to tell our side when Russia uses ballistic missiles."
But Beskrestnov told the BBC that American intelligence continued to be incomplete and inconsistent, and that the US had failed to provide a clear explanation for the issue.
"This looks very strange," he said. "Sometimes we receive this information before the attack, another time we [do] not."
He continued: "And for example, last night we received it, but... one minute before the attack."
However, he said other collaboration with US continues, adding: "Intelligence data keeps flowing, and the issue is solely with the air raid alert component."
Beskrestnov also said the US had given no clarity about who was responsible for the ongoing restrictions to the Starlink internet network and its military service Starshield, which Kyiv uses to provide connectivity for drones, helicopters and military communications.
Last week, Starshield restricted the speed at which mobile units could move while staying connected to the network to 100mph (160km/h).
This has limited Ukraine's ability to shoot down incoming drones or to launch mid-range drone attacks into Russian-occupied areas.
Starlink owner Elon Musk said last week that the US government ultimately controls access to Starshield, which was designed for the Pentagon, suggesting it may therefore be behind the restrictions. Trump has denied involvement.
Beskrestnov said he thought both issues occurring at the same time was "probably" a deliberate move to put pressure on Ukraine.
He told BBC News: "It's probably the United States trying to say [to] us, 'let's have the conversation, negotiation with Russia, you should find the compromise'."
Beskrestnov also said Ukraine had its own radar data to provide some limited warning of incoming attacks, but was urgently looking into using alternative communication systems.
He added: "Now we understand that something begins to happen with Starlink, and we're not sure what will be the next step.
"We understand that we should be prepared for some problems in future. And now we're thinking about an alternative for Starlink, not only for air defence, for communication between our forces, between our staff, for civilians also, because we don't know what we should expect in future regarding Starlink."
Earlier on Monday, US Secretary of State Marco Rubio said there had not been a "pause" to intelligence sharing.
"I don't know where [Zelensky is] getting these things or why he's saying these things to the press," he told reporters on Monday.
Rubio said he could not comment on the incident, adding: "I know a few nights ago there was a software problem involving their early warning system."
The BBC has contacted Starlink for a response.
A White House official said there were no changes to intelligence sharing operations between the US and Ukraine.
The official spoke on background to discuss intelligence matters. Trump is focused on ending the war, the official said, and added that the US has provided more aid to Ukraine than any other country.