Moscow, Russia - Russian President Vladimir Putin called a special meeting of the National Security Council on Thursday, amid speculation that Russia could officially declare war on Ukraine and order a further mobilization of hundreds of thousands of troops for the army.

Kremlin spokesman Dmitry Peskov, when asked by journalists whether the gathering of senior defense officials would upgrade what Moscow continues to call a "special military operation," said: "I don't know, I can't say."

It is a punishable offense in Russia to refer to Moscow's offensive in Ukraine as a war.

Another outcome of the meeting could be greater restrictions on civil rights and steps towards a war and command economy.

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Former Russian president Dmitry Medvedev – now the deputy chair of the Security Council – warned NATO on Thursday against making fighter jets available to Ukraine and maintaining them in Poland, saying that doing so would be tantamount to directly going to war against Russia.

"And anyone who decides on the delivery [repair] of such equipment or means of destruction, as well as foreign mercenaries and military trainers, would have to be considered a legitimate military target," he wrote on Telegram.

Putin accused Ukraine of terror earlier in the day, after reports of fighting in the south-western Russian border region of Bryansk.

It was "another terrorist attack and another crime," the Russian president said during a video conference.

Russia started the war against Ukraine when it invaded its neighbor on February 24, 2022.