KYIV, June 24 (Reuters) – Russia said it would prosecute mercenary boss Yevgeny Prigozhin for armed mutiny after he accused military leaders of killing 2,000 of his fighters, raising the stakes in a growing confrontation with top officials.

As a long-running standoff between him and the Defence Ministry appeared to come to a head late on Friday, the ministry issued a statement denying Prigozhin’s accusations and denouncing them as “informational provocation.”

Kyiv, meanwhile, said the major thrust in its counteroffensive against Moscow’s invasion had yet to be launched. “The main blow is still to come,” Deputy Defence Minister Hanna Maliar told Ukrainian television.

A top Ukrainian general reported “tangible successes” in advances in the south – one of two main theatres of operations, along with eastern Ukraine.

Russian forces there have been fighting alongside mercenaries from the Wagner private military company, whose leader Prigozhin vowed to stop what he called the Russian military’s “evil”. He denied his actions amounted to a coup.

However, Russia’s FSB security service opened a criminal case against him for calling for an armed mutiny, the TASS news agency said, citing the National Anti-terrorism Committee.

Russian President Vladimir Putin was briefed on the developments and “necessary measures are being taken”, Interfax news agency said, citing Kremlin spokesman Dmitry Peskov.

Security was stepped up on Friday night at government buildings, transport facilities and other key locations in Moscow, the state news agency TASS reported, citing a source at a security service.

‘OBEY PRESIDENT,’ GENERAL SAYS

The deputy commander of Russia’s Ukraine campaign, General Sergei Surovikin, told Wagner fighters to obey Putin, accept Moscow’s commanders and return to their bases. He said political deterioration would play into the hands of Russia’s enemies.

“I urge you to stop,” Surovikin said in a