"One cannot fight terrorism while waiting for the permission of whoever," Erdogan told a group of journalists upon returning from a visit to Azerbaijan.

"What will we do if the United States does not do its part in the fight against terrorism? We will get by on our own," he said.

Erdogan's talk of an offensive comes as he threatens to block the NATO membership of Finland and Sweden, which have sought to join the Western alliance out of alarm at Russia's invasion of Ukraine.

Erdogan alleges there is support for Kurdish PKK militants in the two Nordic states, which have launched talks with Ankara in a bid to ease its concerns.

The president said on Monday Turkey would soon launch a new military operation into northern Syria to create a 30-kilometre (19-mile) "security zone" along the border.

The United States on Tuesday warned Turkey against launching a new operation, saying the uneasy NATO ally would be putting US troops at risk.

Turkey has launched three offensives into Syria since 2016 aimed at crushing Syrian Kurdish fighters who assisted the US-led campaign against the Islamic State group, also known as ISIS.

Ankara alleges these fighters are allied with the PKK.

The PKK, blacklisted as a terrorist organisation by Ankara and its Western allies, has waged an insurgency against the Turkish state since 1984.

Erdogan said Turkish, Swedish and Finnish talks in Ankara on Wednesday fell short of Turkey's expectations.

He again accused the two Nordic countries of "supporting terrorism," claiming that Sweden is neither "sincere" nor "honest".