President Vladimir Putin has ordered Wagner mercenary fighters to sign an oath of allegiance to the Russian state days after its leader, Yevgeny Prigozhin, and some of his lieutenants were presumed to have died in a plane crash.

Under the new rules, which took immediate effect on Friday, all “persons entering volunteer formations, and other persons contributing to the fulfillment of the tasks assigned to the Armed Forces of the Russian Federation, other troops, military formations and bodies and taking part in a special military operation must pledge allegiance to the country and military.”

The rules also required that they should take an oath that they will be “devoted to the Russian Federation, to courageously defend its independence and constitutional order.”

The wording of the oath includes a line in which those who swear to it promise to strictly follow the orders of commanders and senior leaders, and is described in the decree as a step to forge the spiritual and moral foundations of theukraine-news" target="_blank" rel="noopener"> defense of Russia. 

Putin’s introduction of a mandatory oath for employees of Wagner and other private military contractors was a clear move to bring such groups under tighter state control.

Earlier this year, the Russian Defense Ministry gave mercenary groups until July 1 to sign army contracts, a move that angered Prigozhin ahead of his failed uprising at the end of June.

Since then Wagner fighters who did not take part in the mutiny have been transferred into the regular Russian army.

Putin signed the decree shortly after Kremlin spokesman Dmitry Peskov told Russian state media that Western suggestions that Prigozhin, the billionaire former food supplier to the Kremlin turned mercenary group mogul, had been killed on government orders were an “absolute lie.”