BRUSSELS (AP) — The European Union is planning the “strongest, the harshest package” of sanctions it has ever considered at an emergency summit Thursday as the Russian military attacked Ukraine and world leaders reacted with outrage at Moscow’s actions.

European Commission President Ursula von der Leyen said that “the target is the stability in Europe and the whole of the international peace order, and we will hold President (Vladimir) Putin accountable for that.”

“We will present a package of massive and targeted sanctions to European leaders for approval,” she said.

EU foreign policy chief Josep Borrell called it the “strongest, the harshest package” ever considered.

“A major nuclear power has attacked a neighbor country and is threatening reprisals of any other states that may come to the rescue,” Borrell said. “This is not only the greatest violation of international law, it’s a violation of the basic principles of human co-existence. It’s costing many lives with unknown consequences ahead of us. The European Union will respond in the strongest possible terms.”

Von der Leyen said the “massive and targeted sanctions” she will put to EU leaders “will target strategic sectors of the Russian economy by blocking the access to technologies and markets that are key for Russia.”

She said the sanctions, if approved, “will weaken Russia’s economic base and its capacity to modernize. And in addition, we will freeze Russian assets in the European Union and stop the access of Russian banks to European financial financial markets.”

Like the first package of sanctions that were imposed when Russia recognized the two breakaway eastern Ukrainian republics, von der Leyen said all Western powers were walking in lockstep.

“We are closely aligned with our partners and allies the United States, the United Kingdom, Canada, but also, for example, Japan and Australia,” she said.

British Prime Minister Boris Johnson said Western allies won’t stand by as Russia attacks Ukraine.

In an early morning call, Johnson told Ukrainian President Volodymyr Zelensky that he was appalled by events in Ukraine, according to a statement released by the prime minister’s office.

“The Prime Minister said the West would not stand by as President Putin waged his campaign against the Ukrainian people,” Johnson’s office said in the statement.

Johnson added that Ukraine was in the thoughts of everyone in the U.K. “during this dark time.”

French President Emmanuel Macron, who had labored until the last minute for a diplomatic solution, said “France firmly condemns Russia’s decision to wage war,” and promised support for Ukraine.

“Russia must end its military operations immediately,” Macron said.

The turmoil from the beginning of a long-feared act of aggression rippled from Europe to Asia. Stock markets plunged, oil prices surged, and European aviation officials warned of a high risk to civilian aircraft over Ukraine, reminding air operators that “this is now an active conflict zone.”

The London Stock Exchange’s leading FTSE 100 index plunged more than 200 points, or 2.7%, within moments of opening following Russia’s actions in Ukraine.

In New York, the U.N. Security Council held an extraordinary emergency meeting meant to dissuade Russia from sending troops into Ukraine. Secretary-General Antonio Guterres’ plea to “give peace a chance” came just as Russian President Vladimir Putin appeared on Russian TV to announce a military operation that he maintained was to protect civilians in Ukraine.

Putin, who said that rebels in eastern Ukraine had asked Moscow for military assistance, warned other countries that any effort to interfere with the Russian operation would lead to “consequences they have never seen.”

As leaders across Asia and Europe scrambled to condemn the attack, explosions were heard in Kyiv and other cities in Ukraine. Nations around the world this week have also imposed a raft of new sanctions on Russia.

Moscow had massed more than 150,000 troops on Ukraine’s borders. On Monday, Putin recognized the independence of two separatist regions in eastern Ukraine and ordered Russian forces there for what he called “peacekeeping.” Guterres at the U.N. disputed that, saying the troops were entering another country without its consent.

German Chancellor Olaf Scholz called Russia’s attack “a terrible day for Ukraine and a dark day for Europe” and “a blatant violation of international law. It cannot be justified by anything.”

In a bulletin Thursday, the European Union Aviation Safety Agency said “there is a risk of both intentional targeting and misidentification of civil aircraft” and that “the presence and possible use of a wide range of ground and airborne warfare systems poses a HIGH risk for civil flights operating at all altitudes and flight levels.”

Asian stock markets were in turmoil.

Market benchmarks in Tokyo and Seoul fell 2% and Hong Kong and Sydney lost more than 3% Thursday. Oil prices jumped nearly $3 per barrel on unease about possible disruption of Russian supplies.

Earlier, Wall Street’s benchmark S&P 500 index fell 1.8% to an eight-month low.

Russia seized Ukraine’s Crimea Peninsula in 2014, and pro-Russia rebels have since been fighting Ukrainian forces in the eastern areas of Donetsk and Luhansk. More than 14,000 people have been killed in the conflict.

Czech Prime Minister Petr Fiala condemned the Russian attack as “absolutely unjustified act of aggression against a sovereign state.” Slovakia Prime Minister Eduard Heger called it “an unjustified barbarian act.”

Many world capitals were trying to determine just what was happening in the tense and fast-changing early moments of a chaotic and violent event.

“We are putting all our effort into collecting the information and comprehending the situation,” Japanese Prime Minister Fumio Kishida said shortly after Putin’s announcement. “It’s important and challenging to secure the safety of Japanese people (in Ukraine). After fully comprehending the situation, we will handle the case properly.”

Asked whether Taiwan would cooperate with the U.S. and like-minded countries to put export controls on semi-conductors and technology products that the self-ruled island is known for, Foreign Ministry spokesperson Joanne Ou said “they were in close coordination” and would take the “appropriate actions in response to help Ukraine and uphold the area’s peace and stability.”

China, which has denounced sanctions against Russia, advised its citizens in Ukraine to stay home and place a Chinese flag in or on their vehicles if they need to travel long distances.

“Social order is chaotic and out of control, especially in the cities where at times of serious unrest, walking on the streets could make one a target of attack, traffic could be stopped at any time and venturing out creates the possibility of running into uncontrollable risks,” the notice said.

China has increasingly aligned its foreign policy with Russia to challenge the West, and has blamed the United States and its allies for provoking Moscow.

Australian Prime Minister Scott Morrison said sanctions against Russia would become law Friday but would not take effect until the end of March. He said the time was needed to give “opportunities for businesses that have had very legitimate operations and business interests in Russia and in the affected territories of Ukraine to be able to make changes to their arrangements.”

Morrison said that financial sanctions and travel bans that target eight members of the Russian Security Council will be a first batch of measures in response to Russian aggression toward Ukraine. Australia will also align with the U.S. and Britain by targeting two Russian banks.

“The reason we’re doing this is there must be a price for the unprovoked, unlawful, unwarranted, unjustified attacks and threats and intimidation that has been imposed by Russia on Ukraine. This cannot be a consequence-free action by Vladimir Putin and the Russian regime,” Morrison said.