What is Turkey's leader Erdogan up to now?

Turkey's leader likes to drive a hard bargain and his unpredictability has become something of a trademark, but what is Recep Tayyip Erdogan up to now?

After months of holding up Sweden's bid for membership of Nato, arguing that Stockholm is guilty of harbouring Kurdish militants, Mr Erdogan suddenly pivots to an entirely unrelated issue: Turkey's longstanding bid to join the European Union (EU).

If Turkey can't join the EU, he seems to be saying, then nor can Sweden join the Nato military alliance.

As far as EU officials are concerned, this is a non-starter. "You cannot link the two processes," was the response of European Commission spokesperson Dana Spinant.

Turkey first applied to join the EU way back in 1987, but its drift towards authoritarianism under President Erdogan brought the accession process to a halt.

Relations had already soured over the 2015 migration crisis, with EU members accusing Mr Erdogan of diplomatic blackmail.

But as an established member of Nato (since 1952), Turkey has power: all Nato members have to agree before any new members are admitted.

President Biden spoke to Mr Erdogan on Sunday, in a last-minute bid to persuade him to drop his opposition to Sweden's membership.

On the eve of the summit in Vilnius, Nato's Secretary General Jens Stoltenberg is convening a meeting between the Turkish president and Swedish Prime Minister Ulf Kristersson.

Most diplomats believe the Turkish leader is using his leverage to extract concessions from the alliance, possibly including the sale of F-16 jets by the US.

Another Nato member (and long-time rival of Turkey), Greece wants assurances that Ankara will not use American-supplied jets to violate its sovereignty.

But since Russia's full-scale invasion of Ukraine in February 2022, Mr Erdogan has also played a unique role as a Nato leader with influence in Moscow.

Turkey has helped the keep the deal alive, despite frequent Russian threats to withdraw.

But Turkey has also angered the Kremlin by supplying armed drones to Ukraine.

Russian officials were also furious at the weekend when Turkey, in a surprise move, allowed five former commanders of the Ukrainian garrison at Mariupol to fly back to Kyiv at the end of a visit by Ukrainian President Volodymyr Zelensky.

Under the terms of a prisoner exchange last year, Russia expected the men to remain in Turkey until the end of the war.

Just what Mr Erdogan's pre-summit posturing means is hard to assess. Over the course of his two decades in power, his allies and rivals alike have come to expect a mercurial approach.

But by holding out on Swedish membership and throwing Turkey's EU ambitions into the mix so late in the day, Mr Erdogan will not have endeared himself to his fellow leaders in Vilnius.