More than two dozen crew of the Russian Black Sea naval fleet's Project 22160 large patrol ship Vasily Bykov who voted against the constitutional amendments that would reset the count of Vladimir Putin's presidential terms say their commanders threaten to have them dismissed from service if they don't change their vote.

That's according to opposition's Aleksey Navalny Headquarters in Krasnodar, reports the Karta Narusheniy [Violations Map] interactive project that is accumulating all incoming reports on signs of fraud during the ongoing referendum.

"Twenty-eight of 63 crew members voted against the amendments. The command of the Novorossiysk Naval Base of the Black Sea Fleet of the Navy demanded that the officers change their minds, threatening to dismiss them," the report reads.

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At the same time, the warship's commander says he will not allow rigging voting results.

As UNIAN reported earlier, Russia is holding a nationwide vote from June 25 to July 1 on proposed changes to the constitution, including an amendment that would allow Putin to seek two more six-year terms as president when his current mandate ends in 2024.

"I do not rule out the possibility of running for office, if this [option] comes up in the constitution. We'll see," Putin was quoted as saying in an interview, Reuters wrote.

The Ministry of Foreign Affairs of Ukraine previously warned that it would be illegal for residents of the occupied territories of Crimea and Donbas who had acquired Russian citizenship to vote in a Russian referendum regarding amendments to the Constitution.