Romania has notified other NATO members that it plans to nominate its president as a candidate for the defense alliance's secretary general, according to European officials.

The nomination of President Klaus Iohannis will complicate other allies' efforts to install outgoing Dutch Prime Minister Mark Rutte as the next chief of the North Atlantic Treaty Organization. But Rutte remains the clear favorite for the post, as the US, Germany and the UK all backed him Thursday to lead the alliance of 31 members once Secretary General Jens Stoltenberg's term ends in October.

Some members on the alliance's eastern flank have withheld a green light as they push for greater representation by the region in senior roles within the organization. The most recent chiefs of the alliance have been from Nordic countries or the Netherlands.

Iohannis' press office didn't respond to phone calls seeking comment. A spokesperson for Rutte said it's up to NATO allies to decide on the next secretary general and declined to comment further.

European and US officials said the Romanian push would probably just prolong the process before Rutte ultimately wins the bid.

"The United States has made it clear to our allies, our NATO allies, that we believe Mr. Rutte would be an excellent secretary general for NATO," White House spokesman John Kirby told reporters Thursday, hours after a UK endorsement of Rutte's candidacy for the post. The German embassy in Washington said in a social media posting that German Chancellor Olaf Scholz supports Rutte, citing his "immense experience, extensive security policy experience and profound diplomatic skill."

The public statements backing Rutte by US and UK officials, including by the British Foreign Office, were viewed by some officials in the alliance as an effort to seal Rutte's bid — and potentially shut out other candidates.

Estonian Prime Minister Kaja Kallas and Krisjanis Karins of Latvia had both previously expressed interest in the role but their countries ultimately held back from nominating them as candidates. Turkey has made clear it would want reassurances from Rutte, including that he wouldn't lean in favor of the bloc's European Union members in the NATO role.

Iohannis said this month that "it would be inadmissible that none of the top jobs being discussed this year would be occupied by someone from east Europe," where NATO members feel "left aside" in the alliance's leadership.

With a requirement for a unanimous decision among allies, NATO countries have been trying to agree on a successor to Stoltenberg by the time foreign ministers meet in Brussels in early April for the alliance's 75th anniversary. Allies want to avoid the role getting caught up in horse-trading over top jobs after the European Union elections in June.

The role of NATO secretary general will be particularly critical in coming years amid growing concerns in Europe about the US commitment to the region's security. Republicans in Congress have blocked funding for Ukraine, and former President Donald Trump has left doubt if he returns to the White House that he would honor the alliance's provision requiring all members to defend any NATO country under attack.

As Russia's war with Ukraine drags on, the next NATO chief will need to balance avoiding any direct spillovers or wider escalation between the alliance and Russia, while also encouraging allies to maintain military and financial support for Ukraine as the public starts to grow weary of the costs.

Romania has significantly boosted its defense spending in the past years and is allocating as much as 2.5% of its GDP for defense spending, surpassing NATO's goal to spend 2%. Iohannis was praised by Trump for the country's spending during his previous term.

Yet his candidacy would be a hard sell considering Romania currently has the deputy secretary general job with Mircea Geoana. Iohannis could also be a potential candidate to replace Charles Michel as European Council president.