Kyiv: Russian President Vladimir Putin announced early on Thursday a military operation in Ukraine to defend separatists in the east of the country. Following the announcement, there has been military action on Ukrainian air bases and the capital city's air defences have been 'neutralised', according to Russian authorities.
Leaders of countries and world organisations around the world have decried the Russian actions and pledged support to Ukraine.
Ukraine's leader Volodymyr Zelensky said Thursday that the country's allies were building a "coalition" against Russian President Vladimir Putin and urged the world to take measures to force Moscow to stop its attack.
"We are building an anti-Putin coalition," Zelensky wrote on Twitter, after talks with the leaders of the US, EU, Britain, Germany and Poland.
"The world must compel Russia to peace," he wrote.
Germany: "A day of shame"
Germany on Thursday blasted Russia's military operation in Ukraine as "a day of shame" and warned that the political and economic consequences for Moscow would be severe.
"Germany condemns in the strongest possible terms this unscrupulous act by President (Vladimir) Putin. Our solidarity goes out to Ukraine and its people," Chancellor Olaf Scholz said in a statement. The world "will not forget this day of shame", Foreign Minister Annalena Baerbock said.
"We will react together with our partners," she said in a statement.
NATO: We stand with the people of Ukraine
NATO chief Jens Stoltenberg on Thursday denounced Russia's "reckless and unprovoked attack" on Ukraine, warning it put "countless" lives in jeopardy.
The ambassadors of the 30-nation alliance were to hold an emergency meeting early Thursday to discuss the Russian attack, with Stoltenberg expected to give a press conference afterwards, a NATO official said separately.
"I strongly condemn Russia's reckless and unprovoked attack on Ukraine, which puts at risk countless civilian lives," Stoltenberg said in a statement.
"Once again, despite our repeated warnings and tireless efforts to engage in diplomacy, Russia has chosen the path of aggression against a sovereign and independent country," Stoltenberg said in a statement. "This is a grave breach of international law, and a serious threat to Euro-Atlantic security. I call on Russia to cease its military action immediately and respect Ukraine's sovereignty and territorial integrity," he said.
Stoltenberg added: "We stand with the people of Ukraine at this terrible time. NATO will do all it takes to protect and defend all allies."
Ukraine is not a member of the 30-nation Western military alliance but its attempt to join has angered the Kremlin leader. Putin has demanded guarantees from NATO and the US that Ukraine would never be granted membership.
Japan condemns Russia
Russia's attack on Ukraine "shakes the foundation of the international order", Japan's Prime Minister Fumio Kishida said Thursday, strongly condemning the military incursion.
"The latest Russia's attack on Ukraine "shakes the foundation of the international order", Japan's Prime Minister Fumio Kishida said Thursday, strongly condemning the military incursion.
"The latest Russian invasion shakes the foundation of the international order, which does not permit unilateral attempts to change the status quo," he told reporters after a meeting of the country's security council.
"We strongly condemn Russia. We will coordinate efforts with the international community, including the United States, and deal with this swiftly," he added.
European leaders condemn the attack
Russia will be held "accountable" for its attack on Ukraine, EU chiefs Ursula von der Leyen and Charles Michel said Thursday.
"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," they each wrote on Twitter.
EU leaders are to hold a snap summit late Thursday.
Italian Prime Minister Mario Draghi on Thursday lashed Russia's attack on Ukraine as "unjustified and unjustifiable," saying Europe and NATO were working on an immediate response.
"The Italian Government condemns Russia's attack on Ukraine. It is unjustified and unjustifiable. Italy is close to the Ukrainian people and institutions in this dramatic moment. We are working with European and NATO allies to respond immediately, with unity and determination," Draghi said in a statement.
"We must immediately respond to Russia's criminal aggression on Ukraine Europe and the free world has to stop Putin," Polish Prime Minister Mateusz Morawiecki wrote on Twitter.
"Today's European Council should approve fiercest possible sanctions. Our support for Ukraine must be real."
UK and allies will 'respond decisively'
British Prime Minister Boris Johnson condemned on Thursday the "horrific events in Ukraine", saying Russia's President Vladimir Putin "has chosen a path of bloodshed and destruction by launching this unprovoked attack".
"The UK and our allies will respond decisively," he tweeted, adding he had spoken to Ukraine's President Volodymyr Zelensky.
US: The world will hold Russia accountable
"The prayers of the entire world are with the people of Ukraine tonight as they suffer an unprovoked and unjustified attack by Russian military forces," the US president, Joe Biden, said shortly after the operation began.
He warned "Russia alone is responsible for the death and destruction this attack will bring."
"The world will hold Russia accountable," he added.
Canada: Clear violation of Ukraine's sovereignty
"These unprovoked actions are a clear further violation of Ukraine's sovereignty and territorial integrity, and of Russia's obligations under international law and the Charter of the UN," Trudeau said in a statement.
He said he would meet with partners from the Group of Seven to shape a collective response, "including by imposing sanctions additional to those announced earlier this week."
"These reckless and dangerous acts will not go unpunished."
UN chief: Stop in the name of humanity
UN Secretary-General Antonio Guterres made a direct, impassioned plea Wednesday to Vladimir Putin to stop - "in the name of humanity" - the Russian military assault on Ukraine. Speaking after an emergency Security Council session, which coincided with the Russian president's announcement of military operations against Ukraine, a clearly emotional Guterres said it was "the saddest day" of his tenure as UN chief.
"President Putin, in the name of humanity, bring your troops back to Russia.