Ukrainian forces said Wednesday its battlefield efforts had been hampered overnight after losing some access to SpaceX’s military-grade satellite Internet service, which has become a lifeline as Kyiv weathers Moscow’s attacks.

Starlink offers Internet connectivity from satellites in low-Earth orbit. Its sister service Starshield, a military version developed for the Pentagon, relies on the Starlink network and has recently been used by Ukrainian forces to strengthen its far-reaching drone strike missions and air defenses.

Serhiy Beskrestnov, a military technology expert who advises Ukrainian President Volodymyr Zelensky, said speed restrictions had been imposed on the “military package” of Starshield services, leading to the “failure” of several military missions. “Our defense forces have not received any warnings about this restriction,” he said. Beskrestnov claimed the restrictions, which he said applied to devices traveling over 100 miles per hour and using Starshield, were “related to the current political situation.” He did not offer further details.

Tensions are high between the U.S. and Ukraine, as Zelensky has been vocal in his disapproval of U.S. President Donald Trump’s plan to import diesel from Russia, despite previous sanctions prohibiting it. The move has also caused a split in Trump’s own party, with several Republican lawmakers urging him to reverse course. After making the deal with Russian President Vladimir Putin last week, Trump announced an “energy cease-fire” between Russia and Ukraine—but Zelensky swiftly accused Moscow of violating any such agreement and Ukraine has, in turn, resumed strikes on Russian refineries, despite pressure from Washington.

Speaking from the U.K., Zelensky said it was a “pity” Ukrainian forces had experienced “difficulties” with Starlink services and intelligence, adding that he was surprised by the developments in Ukraine’s partnership with the U.S. In an interview on Piers Morgan Uncensored Wednesday night, Zelensky suggested he believed Starlink had been slowed down to damage him, and warned “people will die, if attacks will continue and if Starlink will not work … it’s not helpful.” He said he hoped the restriction was only a “mistake,” suggesting it was perhaps “a huge technical problem” at SpaceX.

However, in another interview, Zelensky said: “It was not a technical problem, it was the will.”

SpaceX founder and CEO Elon Musk addressed the matter, insisting that Starlink and Starshield are different. He cited the U.S. authorities as being in control of the latter’s usage determinations.

“Starshield systems are owned and controlled by the U.S. government. Any limits on speed or usage are decided by the U.S. military and ultimately POTUS,” he said on X. “Starlink is a commercial service owned and controlled by SpaceX. Usage of Starlink is limited to civilian or defensive activities and cannot be used for offensive military action, as doing so would be inappropriate for a commercial company.”

A senior U.S. official told Axios that the Trump Administration was not involved in the alleged Starlink limitations.

TIME has reached out to the White House for comment.

Meanwhile, Ukrainian national news agency Ukrinform reported Thursday, citing sources within the Ministry of Defense, that “the work of Starshield in motion has resumed and continues.” A Ukrainian official also told Axios that Ukraine’s Starlink and Starshield satellite services had been restored to full capacity.

TIME has reached out to Ukraine’s Ministry of Defense for comment.

The discourse has nonetheless raised questions about what Starshield is and how uniquely important it has become on the Ukrainian battlefield.

What is Starshield?

Starshield is a program developed by Musk’s SpaceX that draws on the satellite and launch capability behind Starlink, its commercial satellite Internet network, to support national security operations.

According to SpaceX, Starshield is designed for government use, with an initial focus on three areas: Earth observation, communications, and hosted payloads. 

“Starlink is basic interconnectivity, it’s like the Internet. Starshield essentially grows out of the experience of Starlink,” Mark Hilborne, a senior lecturer in defense studies at King’s College London, tells TIME.

But the military value of that connectivity extends far beyond access to the Internet, Hilborne adds.

“In and of itself, satellite communications are not military technology, but it enables the military to communicate and amass a real-time, multi-domain picture of the battlefield, which some argue nobody else actually has at this stage,” he says.

Both systems also offer high-speed connectivity because of the satellite technology underpinning them. 

“Starlink and Starshield are low on the Earth’s orbit, and they have a very high bandwidth, so lots of information can pass through those satellites, with virtually no delay on the signal,” Hilborne says.

There are more than 10,000 satellites in the Starlink network, while Hilborne says Starshield uses “a much smaller number of satellites.” However, the exact number of satellites associated with Starshield remains unknown, with experts telling TIME that such details are closely guarded due to national security considerations.

“They keep the contracting details on these things classified,” says Todd Harrison, a senior fellow at the American Enterprise Institute.

SpaceX, on its website, says Starshield is “designed to support U.S. National Defense use cases for the Department of Defense and other government partners.”

How is Starshield different from Starlink?

While both systems rely on closely related satellite technology, they differ in the services they provide and how they are intended to be used.

“Starshield refers to military services that actually operate through Starlink,” Harrison explains, comparing the services to “two different brands of a cell phone provider, even though your phone calls are going through the same towers.”

Starshield offers additional capabilities designed for military operations, including more advanced encryption and satellite imaging, experts tell TIME.

“It’s got another extra set of capabilities over and above Starlink,” Hilborne says. “They use some of the same technologies, but it would be highly encrypted, and they have different sensors that allow them to image what they call ‘Earth observation.’ That can give a radar imaging of the Earth [which] has advantages over optical pictures.”

Yet experts say the distinction between the two systems is not always clear, particularly given how closely their underlying technology and operations are connected.

How important is Starshield for Ukraine?

Starshield and the satellite communications technology underpinning it have become vital to Ukraine’s military operations against Russia.

Hilborne describes the technology as “highly critical” to Ukraine, explaining that any restrictions could cut communications with military equipment traveling above that speed, leaving operators without the information needed to guide their missions, as once that speed threshold is exceeded, the connection “suddenly cuts off and it’s flying blind,” he says.

The consequences are particularly serious for Ukrainian drone operations, which rely on communications for both strikes against Russian targets and defensive missions against incoming attacks.

“It’s really critical for drones, both the offensive medium range strikes, but also affects Ukraine’s ability to fly defensive drones against the incoming Russian drones,” says Hilborne. 

Beyond its role in drone missions, experts say satellite communications also offer important advantages over other forms of battlefield connectivity.

Harrison notes that “the big benefit of using satellite-based communications is that you can communicate over longer distances in a variety of terrain, and it does have some jam-resistant features to overcome electronic forms of attack.”