ISTANBUL — President Recep Tayyip Erdogan of Turkey said on Monday that the European Union should open the way for Turkey to join the bloc before Turkey allows Sweden to join NATO, adding a surprising new condition that could further stall the military alliance’s efforts to expand.
Mr. Erdogan’s latest demand came a day before the opening of NATO’s two-day annual summit, where leaders, including President Biden, had hoped to secure unanimous approval from member states to allow Sweden to become the 32nd member.
That outcome now appears increasingly unlikely, with Mr. Erdogan posing the main obstacle to Sweden’s membership.
“First, clear the way for Turkey in the European Union, then we will clear the way for Sweden as we did for Finland,” Mr. Erdogan told reporters before traveling to the NATO summit.
Leaders of the European Union and NATO member states are not likely to respond positively, since they are separate organizations that have many overlapping members but entirely different purposes. Turkey applied to join the European Union in 1987, but there has been scarcely any progress in its bid since 2016, when the European Parliament voted to suspend accession talks while criticizing a vast Turkish government crackdown on political opponents after a failed coup against Mr. Erdogan.
NATO’s secretary general, Jens Stoltenberg, said on Monday that he supports Turkey’s ambition to join the European Union, but that it was not among the conditions set by officials from Turkey, Sweden and Finland last year at a NATO summit in Madrid.
“We need to remember that what we agreed in Madrid was a specific list of conditions that Sweden has to meet to be a full member of the alliance, and Sweden has met these conditions,” Mr. Stoltenberg told reporters in Lithuania.
Sweden applied to join NATO last year, after Russia’s full-scale invasion of Ukraine. All NATO nations must agree to admit new members, a rule that has given Mr. Erdogan tremendous leverage to demand concessions.
Turkey has accused Sweden of providing a permissive environment for dissidents whom Turkey considers terrorists, including pro-Kurdish activists and members of a religious group that Turkey has accused of planning the 2016 coup attempt.
In recent months, Sweden has made efforts to meet Turkey’s demands, amending its constitution, passing new counterterrorism legislation and agreeing to extradite several Turks who stand accused of crimes in Turkey. But Swedish courts have blocked other extraditions, and Swedish officials have said that they cannot override their country’s free-speech protections.
Mr. Erdogan has continued to say that Sweden must do more.
A new complication arose late last month after a man publicly burned a Quran at a protest in Stockholm on a major Muslim holiday. Mr. Erdogan criticized Sweden for permitting the protest and said that the Swedish authorities needed to fight Islamophobia, even though that had not been among the issues Sweden had agreed with Turkey to address.
Hungary is the only other NATO member that has yet to approve Sweden’s bid, but Hungarian officials have said that if Turkey’s position changes, they would not obstruct the process. Finland applied at the same time as Sweden, but overcame Turkey’s initial objections and joined the alliance in April.
By linking Turkey’s drive to join the European Union with Sweden’s joining NATO, Mr. Erdogan threw another wrench into the alliance’s negotiations less than 24 hours before NATO leaders are expected to convene in Vilnius, Lithuania, for their annual summit. On Sunday, President Biden spoke with Mr. Erdogan and told him of “his desire to welcome Sweden into NATO as soon as possible,” according to a terse account of the call provided by the White House.
Before traveling to the summit, Mr. Erdogan said again on Monday that Sweden could not expect to join until it had met all of Turkey’s demands with respect to terrorism.
“Nobody should expect compromise nor understanding from me,” he said.
Gulsin Harman contributed reporting.