NATO chief Jens Stoltenberg said on Monday that Turkey has agreed to back Sweden's bid to join the military alliance.

The announcement comes on the eve of NATO's summit in Vilnius, Lithuania, and represents a stunning about-face from Turkish President Recep Tayyip Erdoğan, who had earlier on Monday suggested Sweden could only join the alliance after his country is accepted into the European Union. Erdoğan has stood in the path of Sweden joining NATO for more than a year over a multitude of concerns.

"Glad to announce that after the meeting I hosted with @RTErdogan & @SwedishPM, President Erdogan has agreed to forward #Sweden's accession protocol to the Grand National Assembly ASAP & ensure ratification. This is an historic step which makes all #NATO Allies stronger & safer," Stoltenberg said in a tweet after a meeting in the Lithuanian capital of Vilnius.

This is a breaking story and will be updated.