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.