Former Dutch Prime Minister Mark Rutte has officially become the secretary-general of NATO after a handover ceremony in Brussels.

He takes over from Norway's Jens Stoltenberg, who has led the alliance since 2014.

Following a symbolic handshake and wreath-laying at NATO headquarters, the pair headed to a meeting with bloc ambassadors at the North Atlantic Council for Rutte's official appointment.

The outgoing secretary-general said that the group was in "safe hands" with his successor.

Rutte thanked NATO allies for trusting him with the role. "It is a big job, and I have big shoes to fill," he said.

Stoltenberg took charge of the military alliance the same year Russia annexed Crimea. Only the tenure of Dutch diplomat Joseph Luns, who led NATO for 12 years, surpasses Stoltenberg's stint.

In his first press conference as secretary-general, Rutte called on allies to "significantly increase defense spending" in order to meet NATO's challenges.

An end to the conflict in Ukraine "is vital for peace and security in Europe," he said, adding the cost of Russian President Vladimir Putin getting his way would be far more expensive than aid to Kyiv.

He also called for the alliance to "enhance cooperation with our Indo-Pacific partners," citing the role of China in supporting Putin and as a destabilizing force around the world.

Ukraine, US election loom large

The longtime Dutch prime minister takes over as Russia's invasion of Ukraine approaches the 1,000-day mark.

With Russian forces making advances in eastern Ukraine, it will be a crucial part of his job to shore up support for Kyiv among Western allies as fatigue for the conflict increases.

Rutte said on Tuesday that Ukraine was "on top of our list," as was monitoring the situation in Lebanon.

Ukrainian President Volodymyr Zelenskyy congratulated Rutte online on Tuesday. 

"I wish him every success in this new role and look forward to working productively together to strengthen Euro-Atlantic security and our partnership with the Alliance, as Ukraine continues on its path towards full-fledged NATO membership," Zelenskyy said.

There are also worries among bloc members over the US presidential election in November. Given that the US is NATO's most powerful member, a victory for ex-President Donald Trump could shake the alliance as it did in his first term, when he pressured members to increase defense spending and cast doubt on the bloc's core principle of mutual security.

However, Rutte said during the handover that he was "not worried. I know both candidates very well. I worked for four years with Donald Trump," as Dutch prime minister.

US, UK and Germany congratulate Rutte

US President Joe Biden expressed great confidence in Rutte's role as the leader of the alliance.

"I have full confidence that he will continue to build on our work to create a NATO that is stronger, larger, and more resolute than ever in its mission to create a safer world for our peoples," Biden said in a statement.

UK Prime Minister Keir Starmer on Tuesday congratulated Rutte. 

"I look forward to working together as NATO defends our freedom, including through our steadfast support to Ukraine," Starmer said in a post on X.

The German chancellor Olaf Scholz also welcomed Rutte's appointment.

"The unity of NATO will continue to guarantee our common security in the future. You can rely on my personal support and on the support of the federal government, dear Mark Rutte," he said.

Meanwhile, in Moscow, they believe that despite Rutte's arrival, NATO will continue in the same direction as before.

"Under Rutte's leadership, there will be nothing new or significant in the alliance's policy," Kremlin spokesman Dmitry Peskov said.

es/nm (AP, dpa)