WASHINGTON - An influential British think tank and Ukraine’s military are disputing a report that the U.S. cybersecurity firm CrowdStrike has used to buttress its claims of Russian hacking in the presidential election.

The , asserted that Russians hacked into a Ukrainian artillery app, resulting in heavy losses of howitzers in Ukraine’s war with Russian-backed separatists.

Think Tank: Cyber Firm at Center of Russian Hacking Charges Misread Data

But the (IISS) told VOA that CrowdStrike erroneously used IISS data as proof of the intrusion. IISS disavowed any connection to the CrowdStrike report. Ukraine’s Ministry of Defense also has claimed combat losses and hacking never happened.

Think Tank: Cyber Firm at Center of Russian Hacking Charges Misread Data

A CrowdStrike spokesperson told VOA that it stands by its findings, which, they say, "have been confirmed by others in the cybersecurity community.”

Think Tank: Cyber Firm at Center of Russian Hacking Charges Misread Data

The challenges to CrowdStrike’s credibility are significant because the firm was the first to link last year’s hacks of Democratic Party computers to Russian actors, and because CrowdStrike co-founder Dimiti Alperovitch has trumpeted its Ukraine report as more evidence of Russian election tampering.

Alperovitch has said that variants of the same software were used in both hacks.

While questions about CrowdStrike’s findings don’t disprove allegations of Russian involvement, they do add to skepticism and commentators about the.

The Russian government has denied covert involvement in the election, have concluded that Russian hacks were meant to discredit Hillary Clinton and help Donald Trump’s campaign. An also blamed Russian intelligence services.

On Monday, FBI Director James Comey confirmed at a House Intelligence Committee hearing that his agency has an ongoing investigation into the hacks of Democratic campaign computers and into contacts between Russian operatives and Trump campaign associates. The White House says there was no collusion with Russia, and other U.S. officials have said they’ve found no proof.

VOA News first reported in December that sources close to the Ukraine military and the artillery app’s creator questioned CrowdStrike’s finding that a Russian-linked group it named “Fancy Bear” had hacked the app. CrowdStrike said it found a variant of the same “X-Agent” malware used to attack the Democrats.

CrowdStrike said the hack allowed Ukraine’s enemies to locate its artillery units. As proof of its effectiveness, the report referenced publicly reported data in which IISS had sharply reduced its estimates of Ukrainian artillery assets. IISS, based in London, publishes a highly regarded, annual reference called “The Military Balance” that estimates the strength of world armed forces.

“Between July and August 2014, Russian-backed forces launched some of the most-decisive attacks against Ukrainian forces, resulting in significant loss of life, weaponry and territory,” CrowdStrike wrote in its report, explaining that the hack compromised an app used to aim Soviet-era D-30 howitzers.

“Ukrainian artillery forces have lost over 50% of their weapons in the two years of conflict and over 80% of D-30 howitzers, the highest percentage of loss of any other artillery pieces in Ukraine’s arsenal,” the report said, who had cited figures from IISS.

The report prompted skepticism in Ukraine.

Yaroslav Sherstyuk, maker of the Ukrainian military app in question, called the company’s report “delusional” . CrowdStrike never contacted him before or after its report was published, he told VOA.

Pavlo Narozhnyy, a technical adviser to Ukraine’s military, told VOA that while it was theoretically possible the howitzer app could have been compromised, any infection would have been spotted. “I personally know hundreds of gunmen in the war zone,” Narozhnyy told VOA in December. “None of them told me of D-30 losses caused by hacking or any other reason.”

VOA first contacted IISS in February to verify the alleged artillery losses. Officials there initially were unaware of the CrowdStrike assertions. After investigating, they determined that CrowdStrike misinterpreted their data and hadn’t reached out beforehand for comment or clarification.

In a statement to VOA, the institute flatly rejected the assertion of artillery combat losses.

“The CrowdStrike report uses our data, but the inferences and analysis drawn from that data belong solely to the report's authors,” the IISS said. “The inference they make that reductions in Ukrainian D-30 artillery holdings between 2013 and 2016 were primarily the result of combat losses is not a conclusion that we have ever suggested ourselves, nor one we believe to be accurate.”