NATO failed to immediately move forward with the accession process for Sweden and Finland after Turkey, which earlier had outlined a broad list of complaints with alliance members, blocked the formal acceptance of the applications.

NATO ambassadors met Wednesday morning but couldn’t agree to proceed with the applications after Turkey held up consensus, according to people familiar with the matter. Only after all NATO allies give consent can Sweden and Finland start accession talks with the alliance.

Turkish President Recep Tayyip Erdogan signaled earlier this week that he wouldn’t allow the Nordic nations to join, alleging they support Kurdish militants his government regards as terrorists. He added on Wednesday that his concerns extend beyond Sweden and Finland but also to how other NATO members handle the Kurdish groups.

“Our only expectation from our allies was that they should have approached Turkey’s efforts to protect its borders and establish its security the same way,” he told lawmakers of his ruling AK Party in parliament. “NATO’s expansion is meaningful to the degree our sensitivities are respected.”

President Joe Biden said the U.S. strongly supports the two countries joining NATO and will work to quickly bring them into the alliance.

While the applications are considered, the U.S. “will work with Finland and Sweden to remain vigilant against any threats to our shared security, and to deter and confront aggression or the threat of aggression,” Biden said ahead of a Thursday visit by the Finnish and Swedish leaders.

Prior to Turkey’s concerns, NATO ambassadors were expected to rapidly accept the bids in what was seen as a minor formality and sign the accession protocols within days of their applications. That timing is now set to slip as it’s unclear how long Turkey will dig in over its demands.

“We haven’t lost the possibility of a fast track process,” Finnish President Sauli Niinisto told reporters in Stockholm Wednesday.

A NATO official said the alliance is determined to work through the issues and reach a rapid conclusion.

Turkey is engaged in talks with Sweden and Finland, and NATO members say they’re confident the Turkish concerns can be overcome. However, they could eventually agree with other allies to start the accession process, only to veto down the line.

Finnish Foreign Minister Pekka Haavisto said on Tuesday that he’s in daily contact with Turkish diplomats, and that a meeting in person will be arranged “when the time comes.”

“This is a good day at a critical moment for our security,” the alliance’s secretary general, Jens Stoltenberg, told reporters after he received the bids from Finland and Sweden. “This is a historic moment which we should seize.”

Speaking in an interview on Finland’s YLE TV1, Haavisto called Turkey’s move “a test” of “whether NATO’s open-door policy exists” and signaled that “undemocratic practices, such as oppression, blackmail” aren’t fitting for “an alliance of democratic countries.”

Bringing Sweden and Finland into NATO would fortify the alliance’s defense in the northeast and would mark the biggest shift in Europe’s security landscape to emerge since Russia’s invasion of Ukraine. The traditionally non-aligned countries boast NATO-standard militaries with strong navies and growing defense budgets, as well as major air power.

Finland was driven into the fold of the North Atlantic Treaty Organization by Russia’s Feb. 24 invasion of Ukraine, and pulled neighboring Sweden along. The attack shifted popular opinion overnight in both countries, with policy makers rapidly kicking off the process to join, even as Russia has kept warning the pair with potential consequences.