Turkey's President Recep Tayyip Erdogan agreed Monday to forward Sweden's application to join NATO to his parliament for approval, the alliance's head Jens Stoltenberg said.

After talks in Vilnius with Erdogan and Sweden's Prime Minister Ulf Kristersson, Stoltenberg said Turkey had agreed to move forward, declaring: "This is a historic day."

Earlier, Sweden's possible Nato membership was thrown into fresh doubt when Erdogan said he would only back Sweden's NATO candidacy if the European Union resumes long-stalled membership talks with Ankara.

The mercurial Turkish leader's unexpected demand came on the eve of a landmark NATO summit at which Western leaders want to display unity in the face of Russia's war on Ukraine.

Germany's Chancellor Olaf Scholz quickly called Erdogan's demand unrelated to the issue of giving Sweden the security guarantees afforded by the world's most powerful military organisation.

Erdogan has been blocking Sweden's accession for months because of what he deemed was Stockholm's failure to crack down on Kurdish militants who have been waging a bloody insurgency against the Turkish state.