U.S. spy agencies picked up intelligence in mid-June indicating Wagner mercenary chief Yevgeniy Prigozhin was planning armed action against the Russian defense establishment – which he has long accused of bungling the war in Ukraine – and urgently informed the White House and other government agencies so they were not caught off-guard, several U.S. officials said Saturday.

The exact nature and timing of Prigozhin’s plans were not clear until shortly before his stunning takeover of a military command and tank run toward Moscow on Friday and Saturday, officials said. But “there were enough signals to be able to tell the leadership . . . that something was up,” said one official, who like others spoke on the condition of anonymity citing the matter’s sensitivity. “So I think they were ready for it.”

Over the last two weeks there was “high concern” about what might transpire – whether Russian President Vladimir Putin would remain in power and what any instability might mean for control of Russia’s nuclear arsenal, the official said. “There were lots of questions along those lines,” this person said.

The instability that might result from a Russian “civil war” was the key fear, officials said. In addition to the White House, senior officials at the Pentagon, State Department and in Congress were briefed within the last two weeks on the intelligence, officials said.

A key trigger for Prigozhin, officials said, was a June 10 Russian Defense Ministry order that all volunteer detachments would have to sign contracts with the government. Though the order did not mention Wagner by name, the implication was clear: a takeover of Prigozhin’s mercenary troops, who have proved essential to Russia’s military campaign in Ukraine and have helped secure some of its most notable tactical victories.

Ukrainian military officials also were watching Prigozhin after the June 10 announcement and increasingly believed that he might mobilize his forces against Moscow, said a senior Ukrainian official. Prigozhin had publicly protested the defense ministry’s order, and Ukrainian officials took seriously the possibility that he might move against Russian positions, this person said.

But the timing of a move was unclear, the Ukrainian official said, adding that he was not aware of the U.S. sharing its intelligence with Kyiv on a possible march by Prigozhin and his forces.

Prigozhin is commonly known as “Putin’s chef” owing to his Kremlin catering contracts, and as a master internet propagandist, who is under criminal indictment in the United States for allegedly interfering in the 2016 presidential election. But Prigozhin’s real identity – and future – is wedded to his Wagner mercenary forces, the Ukrainian official said. Leaked intelligence documents obtained by The Washington Post earlier this year show Wagner building a veritable empire in Africa, where Prigozhin provides security for government regimes sometimes in exchange for valuable mineral rights.

In Ukraine, Wagner fighters were able to prevail in the long, bloody battle for the city of Bakhmut only at tremendous cost – 20,000 dead by Prigozhin’s public count, a figure the Ukrainian official found credible. Throughout the fighting, Prigozhin furiously complained that the Russian ministry of defense wasn’t giving him the equipment and supplies he needed to fight. He had threatened to pull out his forces all together. The leaked documents show senior Russian leaders privately fretting about Prigozhin’s rhetorical attacks, which they found both credible and undermining of their authority.

“Tensions between the Wagner Group and the Russian Ministry of Defense are no secret,” said a senior administration official, who did not comment on U.S. intelligence. “We have all seen Mr. Prigozhin publicly criticize, warn, and even threaten the Russian military on any number of occasions.”

U.S. intelligence agencies believe that Putin also was informed that Prigozhin was plotting something. And though it is not clear precisely when he was told, it was “definitely more than 24 hours ago,” the U.S. official said.

It remains unclear why Putin did not take action to thwart Prigozhin’s takeover of the military command or his move on Moscow. The Wagner chief got to within 120 miles of the capital before he turned around after striking a deal, brokered by Belarusian President and Putin ally Alexander Lukashenko. The deal calls for dropping criminal charges against Prigozhin, lodged on Friday after he accused Russian Defense Minister Sergei Shoigu of ordering an attack on his mercenaries and issued a call to “put an end” to the minister’s leadership.

Putin’s inaction reflected a lack of high-level coordination in the Russian government and likely internal rivalries, U.S. officials surmise.

Prigozhin faced little resistance when he and his forces marched into Rostov-on-Don and took control of the Southern Military District headquarters there, Western and U.S. intelligence officials noted, calling that an indication he enjoys some level of support among regular military forces as well as Russia’s security services.

“If Prigozhin intended to drive a wedge between the command of Russian Federation Armed Forces and the Kremlin he failed,” said the senior Western official, meaning that the 24-hour rebellion does not appear, for now, to have triggered a broader rupture between Putin’s inner circle and the military leaders Prigozhin detests.

Analysts nonetheless say that this appears to be the most serious challenge to Putin in the more than two decades he has served as Russian paramount leader. The last significant challenge was in 2011, when tens of thousands of Russians turned out in Moscow to protest what European and U.S. officials concluded were flawed parliamentary elections.

“But having an armed group make it to within [120] miles of Moscow is pretty serious,” the first U.S. official said.

Intelligence analysts are watching to see what comes next. Though Prigozhin has stood down, Putin will certainly be seen as weakened, officials said. Images of Wagner tanks rolling along the Russian M4 highway toward Moscow played on social media and Putin made a televised speech to the nation on Saturday saying there had been an “armed insurrection,” and accused Prigozhin of betraying Russia without mentioning him by name.

Members of the Russian elite will question his leadership, asking how he could have let this happen and why he didn’t stop it earlier, officials say. “This probably has given ordinary Russians a scare,” said the first U.S. official.

As for Prigozhin, the Kremlin said Saturday he was going to Belarus as part of the deal worked out by Lukashenko. His future beyond that is unclear. He has a solid core of loyal troops, and many of those who fought and died in Ukraine were convicts who hoped to win freedom by going to battle.

Officials said they were sure he’d still be seen as the leader of Wagner.