Ukraine's intelligence chief claimed Wagner's mutineers almost reached a Russian base holding Cold War-era nuclear bombs small enough to be carried in backpacks

• Ukraine's spy chief claimed the Wagner Group almost reached a Russian nuclear base in late June.
• The mercenaries had been rebelling under Yevgeny Prigozhin, who ordered a march on Moscow.

Ukraine's intelligence chief said Wagner mercenaries nearly reached a Russian nuclear base as they rebelled against the Kremlin in late June, Reuters reported on Monday.

The Ukrainian intelligence officer, Kyrylo Budanov, told the outlet that the base, called Voronezh-45, contained a stockpile of small, Soviet-era nuclear bombs, each of which could be carried by a single man with a backpack.

"Because if you are prepared to fight until the last man standing, this is one of the facilities that significantly raises the stakes," Budanov said, per Reuters.

Budanov did not say how he obtained this information, nor did he provide evidence for his claim, Reuters reported.

He is the first official to publicly make such assertions, though matching allegations were made at the time of Wagner's revolt by the pro-Kyiv partisan group Atesh, which operates in Russian-occupied Ukrainian territories.

Reuters also obtained similar information from an anonymous source in the Kremlin, who said Wagner forces entered a "zone of special interest" and "agitated" the US because a nuclear stockpile was held there.

The Pentagon said at the time that it believed the rebellion was an internal issue and presented no issues for the US regarding Russia's nuclear arsenal.

However, The Washington Post on June 24 cited an unnamed US official saying there was "high concern" among US agencies about whether Russia's nuclear arsenal might come into play if a Moscow-Wagner civil war broke out.

In its Monday report, Reuters said it tracked surveillance footage and civilian-posted videos in the region of Voronezh, which show how some Wagner fighters broke off to move east toward Voronezh-45 — partially corroborating Budanov's claim.

Wagner's rebelling forces would have passed through Voronezh on their way to Moscow from the city of Rostov-on-Don, which they occupied on June 24.

While Reuters could only track the fighters until they were around 70 miles from the base, Budanov claimed but did not provide evidence that they got much closer despite heavy resistance from Russian troops and intended to seize the nuclear munitions inside.

It's unclear how close they got to their intended destination. Prigozhin called off his rebellion on June 24, as Belarusian leader Alexander Lukashenko said he helped the Wagner boss and Russian leader Vladimir Putin reach an agreement.

Russia does not say if Voronezh-45 houses nuclear weapons, but the base is believed by outside observers like the Russian Nuclear Forces Project to be one of the Kremlin's 12 main storage sites.

As for the small nuclear devices described by Budanov, the Soviet Union once fielded an arsenal of low-yield, portable weapons colloquially known as "suitcase nukes," which could be carried by a single person. The US also designed such portable weapons during the Cold War.

But even if Voronezh-45 does contain such munitions, it's unlikely the bombs would still be effective, as production and regular maintenance for these weapons were discontinued by Moscow and Washington decades ago.

It's also unlikely that troops from a private military company like Wagner would have possessed the knowledge to arm and deploy nuclear weapons on their own.

Russia's Ministry of Defense did not immediately respond to a request for comment sent outside regular business hours.