Explosions were heard in the Ukrainian capital Kyiv and other parts of the country soon after Russian President Vladimir Putin announced a military operation in the neighbouring country on Thursday, media reports said.

After weeks of intense diplomacy, the US, UK and their allies imposed a number of economic sanctions on Russia and said more would follow if it invaded Ukraine. However, the sanctions did not deter Putin who had massed around 200,000 troops along the borders of Ukraine.

In a surprise television announcement around 6:00 am in Moscow, Putin said, "I have made the decision of a military operation" in Ukraine.

Ukraine’s Foreign Minister Dmytro Kuleba said “full-scale invasion” of Ukraine was underway and that peaceful Ukrainian cities were under strike.

“This is a war of aggression. Ukraine will defend itself and will win. The world can and must stop Putin. The time to act is now.”

Putin has just launched a full-scale invasion of Ukraine. Peaceful Ukrainian cities are under strikes. This is a war of aggression. Ukraine will defend itself and will win. The world can and must stop Putin. The time to act is now.

— Dmytro Kuleba (@DmytroKuleba) February 24, 2022

Confirming the attack on Ukraine, the country’s Deputy Interior Minister, Anton Gerashchenko, said missiles have hit military headquarters, airports, military warehouses, near Kyiv, Kharkiv, Dnieper.

“From this day, there is a new geopolitical reality in the world,” Gerashchenko said in a statement posted on his official Facebook page.

>>Also Read | Russia-Ukraine crisis: Donald Trump lauds Vladimir Putin’s ‘genius’ move on Ukraine

Condemning the attack, US President Joe Biden said the world would hold Russia alone responsible for the death and destruction brought about by the attack.

“The United States and its Allies and partners will respond in a united and decisive way,” the President tweeted.

Russia alone is responsible for the death and destruction this attack will bring, and the United States and its Allies and partners will respond in a united and decisive way.

The world will hold Russia accountable.— President Biden (@POTUS) February 24, 2022

Soon after the attack, United Nations Secretary-General Antonio Guterres appealed to the Russian President to stop the offensive.

“In the name of humanity, bring your troops back to Russia. This conflict must stop now,” Guterres said in a tweet.

Under the present circumstances, I must change my appeal:

President Putin, in the name of humanity, bring your troops back to Russia.This conflict must stop now.— António Guterres (@antonioguterres) February 24, 2022

NATO secretary general Jens Stoltenberg said Russia’s reckless attack would put countless civilian lives at risk.

“This is a grave breach of international law & a serious threat to Euro-Atlantic security,” Stoltenberg said.

I strongly condemn #Russia’s reckless attack on #Ukraine, which puts at risk countless civilian lives. This is a grave breach of international law & a serious threat to Euro-Atlantic security. #NATO Allies will meet to address Russia’s renewed aggression. https://t.co/FPpyuzmUXD

— Jens Stoltenberg (@jensstoltenberg) February 24, 2022

He said NATO allies would conduct a meeting soon to tackle the consequences of Moscow's "aggressive actions".