Will hold Kremlin accountable, says EU chief

Terming Russia's military operations as an 'unjustified attack', EU chief Ursula von der Leyen strongly condemned Moscow's actions in Ukraine and said the bloc will hold the Kremlin accountable.

"We strongly condemn Russia's unjustified attack on Ukraine. In these dark hours, our thoughts are with Ukraine and the innocent women, men and children as they face this unprovoked attack and fear for their lives. We will hold the Kremlin accountable," Leyen tweeted.

Separately, NATO Secretary-General Jens Stoltenberg condemned Russia's actions, saying that Moscow's operation in Donbas violates international law.

"I strongly condemn Russia's reckless attack on Ukraine, which puts at risk countless civilian lives. This is a grave breach of international law and a serious threat to Euro-Atlantic security. The NATO allies will meet to address Russia's renewed aggression," the NATO chief tweeted.

Ukrainian President Volodymyr Zelensky on Thursday morning introduced martial law, urging citizens to remain calm amid Russia's military operations.

In a brief video address, Zelensky said Russia has announced a special military operation in the Donbas region and is conducting strikes on its military infrastructure and border guards.

"We're introducing martial law in the whole territory of our country," Zelensky said in a statement. He also informed that he spoke with US President Biden and Washington has already started mobilizing international support.

Ukraine has closed the airspace for civilian aircraft "due to the high risk of aviation safety."

"The Joint Civil-Military Air Traffic Management System of Ukraine on the use of Ukraine's airspace, in accordance with the requirements of the Air Code of Ukraine and the Regulations on the use of Ukrainian airspace, has taken urgent measures to close Ukraine's airspace to civilian airspace users," the authority said in a statement.

Multiple explosions were heard near the main airport in the Ukrainian capital of Kiev soon after Russia announced a military operation in Ukraine, media reports said on Thursday.

Several reports indicate several explosions in the Boryspil area to the east of the capital, CNN reported.