MADRID • An unstable world could get even more dangerous if NATO does not remain strong and united, the head of the alliance said Thursday at the end of a summit where Western leaders labeled Russia “a direct threat” to the security of their nations.

During their three-day meeting in Madrid, NATO members confronted a geopolitical landscape marked by big-power competition and myriad threats, from cyberattacks to climate change. The leaders cast their sights around the world — drawing a rebuke after accusing China of posing “serious challenges ” to global stability. But Russia’s invasion of Ukraine dominated the summit.

“We live in a more dangerous world and we live in a more unpredictable world, and we live in a world where we have a hot war going on in Europe,” NATO Secretary-general Jens Stoltenberg said. “At the same time, we also know that this can get worse.”

That is why the Western military alliance has a “core responsibility” to keep the war in Ukraine from spilling into other countries while making clear to Moscow that it would “protect every inch of NATO territory,” Stoltenberg said.

That territory is set to grow. At the summit, NATO leaders formally invited Finland and Sweden to join the alliance, after striking an agreement to end opposition from Turkey.

However, Turkish President Recep Tayyip Erdogan said he could still block the Nordic countries’ membership, if the Nordic pair do not keep their promises.

If the accession is approved by all 30 member nations, it will give NATO a new 800mile border with Russia.

Russian President Vladimir Putin warned he would respond in kind if Sweden or Finland agreed to host NATO troops and military infrastructure.

He said Russia would have to “create the same threats for the territory from which threats against us are created.”

Estonian Prime Minister Kaja Kallas said Putin’s threats were “nothing new.”

“Of course, we have to expect some kind of surprises from Putin, but I doubt that he is attacking Sweden or Finland directly,” Kallas said.

NATO leaders turned their gaze south for a final summit session Thursday focused on Africa’s Sahel region and the Middle East, where political instability — aggravated by climate change and food insecurity sparked by the war in Ukraine — is driving large numbers of migrants toward Europe.

The U.S. and other Western nations also are seeking to counterbalance the growing influence of China and Russia in the developing world. Stoltenberg said “Moscow and Beijing are using economic leverage, coercion and hybrid approaches to advance their interests in the region.”