NATO on Wednesday condemned Russia's "appalling cruelty" in Ukraine while pledging long-term support for Kyiv.

"Ukraine can count on us for as long as it takes," NATO chief Jens Stoltenberg said at a summit in Madrid.

"President [Vladimir] Putin's war against Ukraine has shattered peace in Europe and has created the greatest security crisis in Europe since the Second World War," said Stoltenberg.

NATO leaders are in the Spanish capital for the second day of a summit that Stoltenberg said would be "historic and transformative," as the alliance revamps its strategy in response to Russia's invasion of its neighbor.

Stoltenberg said Russia's aggression is presenting the most "serious security crisis" in decades and the "biggest challenge" NATO has faced in its history.

NATO's new Strategic Concept

The military alliance's statements came as part of a new  strategic concept,which was unveiled on Wednesday.

Member states agreed to increase the number of soldiers in a high state of readiness from 40,000 to 300,000, while also deploying more heavy weaponry in Baltic states and Poland.

Stoltenberg said leaders had also agreed on a comprehensive assistance package for Ukraine which would include secure communications, fuel and medical supplies, equipment to counter mines and also anti-drone systems.

There would also be more training for Ukrainian forces on more modern weapons systems.

The strategic concept is updated around every 10 years to reaffirm "NATO's values and purpose, and provides a collective assessment of the security environment," according to the NATO website.

Russia's invasion of Ukraine has galvanized a coordinated NATO response and reinvigorated the alliance, which French President Emmanuel Macron had called "brain dead" in 2019. US former-President Donald Trump also repeatedly questioned the value of NATO and mulled withdrawing the United States from the alliance during his presidency.

NATO invitation extended to Sweden, Finland 

After decades of neutrality, Finland and Sweden are now set to join the alliance after Turkey removed its objections to the Nordic countries' membership on Tuesday evening. 

And within 24 hours, NATO leaders collectively declared, "Today, we have decided to invite Finland and Sweden to become members."

Ratification in allied parliaments could take up to a year, but once completed, Finland and Sweden will be covered by NATO's Article 5 collective defense clause.

"We will make sure we are able to protect all allies, including Finland and Sweden," Stoltenberg said.

NATO leaders also said the alliance would bolster the defenses along the bloc's eastern flank. This includes having more combat-ready troops and pre-positioned military equipment stationed in eastern Europe.

US to increase forces in Europe

Earlier on Wednesday, US President Joe Biden said that NATO is needed more today "than it ever has been," and that the alliance will be "strengthened in all directions across every domain — land, air and sea."

The US will bolster its forces in Europe with two more warships stationed in Spain, two additional fighter jet squadrons to the UK and a new army headquarters in Poland, Biden said. 

The summit will send out the "unambiguous message" that NATO is strong and united, he added.

Ukraine presses for more weapons

Ukrainian President Volodymyr Zelenskyy addressed the 30 NATO leaders by video link. He called on NATO countries to provide Ukraine with modern missile and air defense systems to counter Russia's artillery.

"This is not a war being waged by Russia against only Ukraine. This is a war for the right to dictate conditions in Europe, for what the future world order will be like," he said.

"That is why it is absolutely necessary to support Ukraine, even now, with weapons, finances and political sanctions against Russia, which will stop its ability to pay for the war."

China listed in new NATO strategy

NATO's new strategic concept includes language identifying the growth of China's military as a long-term strategic challenge.

"The People's Republic of China's (PRC) stated ambitions and coercive policies challenge our interests, security and values," the concept, published at the summit, said. 

"It strives to subvert the rules-based international order, including in the space, cyber and maritime domains."

It accused Beijing of targeting NATO members with its "malicious hybrid and cyber operations and its confrontational rhetoric."

On Wednesday morning, Stoltenberg highlighted that in the previous NATO security concept from 2010, China is "not mentioned in a single word."

"China is not an adversary, but of course we need to take into account the consequences of our security when we see China investing heavily in new modern military capacity."

kb, jsi, wmr/sms (AP, Reuters, AFP, dpa)