"Top officials in NATO’s leading countries have been making aggressive statements against our country. For this reason, I give orders to the defense minister and chief of the General Staff to introduce a special combat service regime in the Russian army’s deference forces," Putin told a meeting with Defense Minister Sergey Shoigu and Chief of the General Staff Valery Gerasimov in the Kremlin on Sunday.

Putin stressed that the Western countries were also taking unfriendly actions against Russia in the economic sphere, reported Tass."I am referring to the illegitimate sanctions, which are very well-known to everybody," he said.

NATO has termed Putin's nuclear readiness move as "dangerous rhetoric" NATO Secretary General Jens Stoltenberg told CNN’: “If you combine this rhetoric with what they're doing on the ground in Ukraine, waging war against an independent sovereign nation, conducting a fully-fledged invasion of Ukraine, this adds to the seriousness of the situation."

The European Union meanwhile has announced that it wants to ship arms to Ukraine, which would be for the first time in its history.

European Commission President Ursula von der Leyen  Sunday said that the European Union will ban all "Russian-owned, Russian registered or Russian-controlled aircraft," including the private jets of oligarchs, from its airspace. EU also banned the Russian state media like Russia Today and Sputnik.

"They won’t be able to land in, take off or overfly the territory of the EU.  Including the private jets of oligarchs," von der Leyen said.

"The state-owned Russia Today and Sputnik, and their subsidiaries, will no longer be able to spread their lies to justify Putin’s war," she added.

"We are developing tools to ban their toxic and harmful disinformation in Europe," she said.

Kharkiv Battle

Meanwhile, as Russia tried to get control over Ukraine's second largest city Kharkiv, the Ukrainian forces said they have repulsed the move engaging in fierce clashes with the invading forces.

BBC quoted regional governor Oleh Synehubov saying the city was "now rid of Russian troops - after street-to-street fighting."

Image: ABC screenshot of Kharkiv

Thousands spent the night in basements and shelters, with intense shelling described by one resident as "something like Star Wars above your head", reported BBC.

Ukraine agrees to talk

Earlier on Sunday, Ukraine  agreed to meet the Russian delegation at the Ukrainian-Belarusian border, near the Pripyat River.

"We agreed that the Ukrainian delegation would meet with the Russian delegation without preconditions on the Ukrainian-Belarusian border, near the Pripyat River", Ukrainian President Volodymyr Zelensky wrote on his official Telegram channel.

"President of Belarus Alexander Lukashenko has taken responsibility for ensuring that all planes, helicopters and missiles stationed on Belarusian territory will remain on the ground during the Ukrainian delegation's travel, talks and return," he added.