Shortly after President Vladimir Putin's announcement, Russia began an all-out military operation on Ukrainian territory.

In a statement, the Ukrainian Border Guard confirmed that Russian troops had entered the Kiev region of Belarus to carry out a Grad missile attack on military targets.

Flight of unidentified helicopters in low-altitude groups in Kiev suburb, Ukrainian capital

Emergency devices in Ukraine reported the crash of a military aircraft near Kiev with 14 people on board.

NATO members agreed to strengthen NATO ground, sea and air forces on its eastern side near Ukraine and Russia, while the Kremlin confirmed that military operation in Ukraine would continue as long as necessary.

Black smoke was seen rising above the Ministry of Defence intelligence headquarters in central Kiev.

According to the Ukrainian command, some army command posts were hit by Russian missiles as Moscow launched a military operation into the country.

Two cargo ships suffered a Ukrainian missile strike in the Sea of Azov, causing casualties, Russian news agency Tass reported.

Poland called on NATO to activate Article 4 calling for emergency consultations in the event of a threat to a Member State after Russia launched an attack on Ukraine.

In a statement, the Russian Ministry of Defence denied the loss of Russian aircraft or the destruction of armoured vehicles in Ukraine.

The statement explained that "the Russian armed forces do not strike Ukrainian cities or threaten civilians."

The Russian army confirmed that it had destroyed anti-aircraft defence systems and made Ukrainian air bases "out of service."

Russian news agencies quoted by the Russian Ministry of Defence indicated that "the military infrastructure of the air bases of the Armed Forces of Ukraine has become out of service and the air defence systems of the Armed Forces of Ukraine have been destroyed."

The Ukrainian military said the air force was trying to repel a Russian air attack, adding that reports of Russian troops landing in Odessa were false.

The Ukrainian authorities suspended the websites "for fear of infiltration attacks."

In a statement, the Ukrainian military had announced the shooting down of 5 Russian air defenses and helicopters in Lugansk.

The service of the Ukrainian Border Guard confirmed attacks on border units, patrols and checkpoints, carried out using artillery, heavy materiel and small arms.

The Ukrainian border had been attacked by Russia and White Russia, along with Crimea.

He heard explosions in the capital Kiev and several Ukrainian cities near the front line, and along the country's coast, at dawn Thursday.

Explosions were also heard in Kharkiv, Ukraine's second city, 35 kilometres from the border with Russia.

Four powerful explosions were heard in Kramatorsk, the capital of the Ukrainian government in the east of the country, which has been in conflict with pro-Russian separatists for years.

Before that, Doi had also heard explosions in the city of Odessa on black beagles, and ambulance sirens on the streets of the Ukrainian capital.

Explosions were also heard in coastal Maribol, while residents in the city near the border with Russia reported hearing gunfire on the outskirts of the eastern city.