Russia’s Defense Ministry announced early Monday its forces had thwarted a large Ukrainian attack in the eastern province of Donetsk, though it’s unclear if this was the start of a Ukrainian counteroffensive.

The ministry, in a rare early morning video, said its forces pushed back a “large scale” Ukrainian assault on Sunday at five points in southern Donetsk, one of four Ukrainian regions Russia illegally annexed last fall, Associated Press reported.

“The enemy’s goal was to break through our defenses in the most vulnerable, in its opinion, sector of the front,” said the ministry’s spokesman, Igor Konashenkov. “The enemy did not achieve its tasks. It had no success.”

Konashenkov said 250 Ukrainian personnel were killed, and 16 Ukrainian tanks, three infantry fighting vehicles and 21 armored combat vehicles were destroyed.

Ukraine didn’t comment, and often waits until the completion of its military operations to confirm its actions, imposing news blackouts in the interim. It was unclear why the Russian Defense Ministry waited until Monday morning to announce the attack, which it said started Sunday morning.

For months, Ukrainian officials have spoken of plans to launch a spring counteroffensive to reclaim territory Russia has occupied since invading Feb. 24, 2022, as well as the Crimean Peninsula it seized in 2014.

But they’ve given confusing signals about what would constitute a counteroffensive — preliminary, limited attacks to weaken Russian forces and military facilities or a full-fledged simultaneous assault across the entire 1,100-kilometer front line.

The Russian Defense Ministry spokesman said Ukraine used six mechanized and two tank battalions in the attack, and it released a video claiming to show destruction of some of the equipment in a field.

Russian mercenary boss Yevgeny Prigozhin, who has been arguing with top military brass for months, on Friday escalated the feud by accusing pro-Moscow forces of trying to blow up his men.

Prigozhin’s Wagner Group troops have largely pulled back from the eastern Ukrainian town of Bakhmut, most of which they captured last month after taking heavy casualties, and handed over their positions to regular Russian forces, Reuters reported.

Prigozhin, writing on Telegram, said his men had discovered a dozen locations in rear areas where defense ministry officials had planted various explosive devices, including hundreds of anti-tank mines. When asked why the charges had been set, the officials indicated it was an order from their superiors.

“It was not necessary to plant these charges in order to deter the enemy, as it (the area in question) is in the rear area. Therefore, we can assume that these charges were intended to meet the advancing units of Wagner,” he said.

None of the charges went off and no one was hurt, he said, adding: “We assume this was an attempt at a public flogging.”

Russia’s defense ministry was not immediately available for comment.

Prigozhin, who regularly complained his men were not given enough ammunition for the assault on Bakhmut, said on Wednesday that he had asked prosecutors to investigate whether senior Russian defense officials had committed any “crime” before or during the war in Ukraine.

U.S. President Joe Biden predicted on Thursday Sweden will join NATO “soon”, speaking at the U.S. Air Force Academy days after he hinted at a possible deal to overcome Turkey’s opposition to admitting the Nordic country to the alliance, Reuters reported.

Biden, in a flag-waving commencement address in Colorado Springs, Colorado, warned graduates they will enter service in an increasingly unstable world, citing challenges from Russia and China.

Biden, 80, who stood for much of the hours-long ceremony to shake hands with graduates, appeared to trip over something and fell to his knees towards the end. He was assisted to his feet and walked to his seat unaided.

On Monday, Biden spoke to Turkish President Recep Tayyip Erdogan to congratulate him on his re-election. Biden told reporters Erdogan repeated Ankara’s desire to buy F-16 fighter jets from the United States, while Biden urged Ankara to drop its objection to Sweden’s joining NATO, read the report.

In his commencement speech, Biden said NATO is stronger in spite of Russian President Vladimir Putin’s attempt to crack the alliance with his invasion of Ukraine. It is bolstered further, he said, by the recent admission of Finland, “and soon, Sweden.”

“It will happen, I promise you,” he said, but provided no details.

On Monday, Biden said he would speak to Erdogan again soon. NATO’s annual summit is in Vilnius, Lithuania, in July, Reuters reported.

On Tuesday, U.S. Secretary of State Antony Blinken urged Turkey to immediately finalize Sweden’s accession to NATO, saying the country had already taken significant steps to address Ankara’s objections to its membership.

The White House has denied that Biden is pursuing a deal with Turkey to lift its opposition in exchange for F16s.

The 80-year-old president, who is seeking re-election in 2024, stood, throughout the presentation of more than 900 diplomas despite the relatively thin mountain air, shook hands and gave sharp salutes to the blue-uniformed graduates. His fall came at the end of the individual salutes. The Air Force Academy stands at 7,258 feet (2,212.3 meters) above sea level, Reuters reported.

Biden made clear the United States would not back down from the challenge posed by China amid deep strains in the relationship.

“The United States does not seek conflict or confrontation with China. China and the United States should be able to work together where we can to solve some global challenges, like climate,” he said.

“But we are prepared for vigorous competition,” he said, adding the United States would stand up for its interests and that of its partners.

The president emphasized U.S. support for Ukraine in the war with Russia, Reuters reported.

“The American people’s support for Ukraine will not waver,” Biden said.