On Sunday, President Vladimir Putin put Russia's nuclear deterrence forces on high alert due to a flurry of retaliatory measures by the West.
The United States stated that it was a very dangerous way of escalating the war. The US added that Russia's invasion of Ukraine, being a serious threat to Europe since World War II, has resulted in a large-scale and concerted Western response.
The attack started less than four days ago. However, it triggered Western-led political, strategical, economical and corporate sanctions unprecedented in their extent and coordination.
"With this war on Ukraine, the world will never be the same again. It is now, more than ever, the time for societies and alliances to come together to build our future on trust, justice and freedom. Might does not make right. Never did. Never will'', EU foreign policy chief Josep Borel said.
On Sunday, the 27-nation European Union decided to supply weapons to a country at war. Reuters reported that Ukraine would receive 450 million euros ($507 million) of weaponry.
At a Sunday news conference, Borrell said that EU's support would include providing Ukraine with fighter jets.
The Russian ruble plunged by nearly 20% against the US dollar on Monday after Western countries unveiled tough sanctions, blocking some banks' access to the international payment system SWIFT.
Nearly 400,000 civilians, mainly women and children, have fled to neighboring countries since the war began in Ukraine. On Sunday, hundreds of people were trapped in Kiev waiting for a train to take them west, away from the fighting.
The EU and Canada have closed their airspace to Russian airlines, forcing Russian carrier Aeroflot to cancel all flights to European destinations.
Moreover, the United States and France urged their citizens to consider leaving Russian territory immediately.
The EU also banned Russian media outlets Russia Today and Sputnik.
The British Petroleum Company Plc, which was the largest investor in Russia at $25 million, exited its shareholding in Russia's oil company Rosneft PJSC. Accordingly, its shares are plunging.
Germany has already halted the Nord Stream 2 Baltic Sea gas pipeline project.
US Ambassador to the United Nations Linda Thomas-Greenfield urged Russia to tone down its "dangerous rhetoric regarding nuclear weapons".
As part of the toughest economic sanctions, the United States and Europe said on Saturday that they would expel key Russian banks from major global markets.
The president of Switzerland stated that he would follow the EU on Monday in sanctioning Russia and freezing Russian assets.
The 193-member UN General Assembly will hold an emergency session in New York today.
Protests against Russia's invasion of Ukraine are continuing all over the world.