Erdogan’s comments came hours before he was due to receive Ukrainian President Volodymyr Zelensky for talks focused on Russia’s invasion and the US-led military bloc’s expansion.

Nato member Turkey’s resistance to accepting Sweden into the alliance has irritated Washington and Brussels, which argue that Stockholm has done enough to address Ankara’s concerns.

Erdogan is blocking the candidacy because of a longstanding dispute about Stockholm’s perceived lax attitude toward alleged Kurdish militants living in the Nordic country.

Erdogan on Friday reaffirmed his concerns, asking “how a country with terrorists on the streets… can contribute to Nato”.

But he also did not rule out the possibility of giving his green light to Sweden’s membership, which he will discuss with Swedish Prime Minister Ulf Kristersson on Monday at Nato-organised talks.

“On Tuesday in the leadership summit to be held in Vilnius, we will be discussing (Turkey’s concerns) with our partners. We will make the best decision, whatever it is,” he said in televised remarks.

Zelensky called on Nato to resolve the issue of Sweden and Ukraine’s membership bids, saying indecision is threatening the strength of the alliance and global security.

Battling a Russian invasion for more than 16 months, Kyiv has expressed increasing frustration with its Western allies over guarantees that it will one day join the alliance.

He spoke on a visit to Slovakia before he was due to head to Turkey for talks with Erdogan.

“I think there is not enough unity on this,” Zelensky said during a press conference.

“This is a threat to the strength of the alliance,” the Ukrainian leader said, adding: “This is very important for the security of the whole world.”

Zelensky said Kyiv expected “positive results or at least some steps towards the positive outcome” at a Vilnius summit next week.

“I believe that the situation with the aggressor, with Russia, depends on this,” he said.

“Because Russia is counting on the world to show weakness and disunity in the Alliance, and this cannot be allowed,” he added.

Zelensky also said he expected “defence packages” at the summit. “And not just promises, but with clear deadlines.”