Ankara on Saturday issued a travel warning for the United States and Europe in seeming retaliation for similar alerts by Western powers for Turkey.

The United States and major European countries have advised their citizens against attending mass events and to avoid tourist hotspots in Turkey.

Their warnings came during a spike in diplomatic tensions linked to Turkey's refusal to let Sweden and Finland join the US-led NATO defence bloc.

Ankara has been most recently outraged by anti-Islamic protests by a far-right extremist who was allowed to burn the Koran outside the Turkish embassies in Stockholm and Copenhagen.

The Turkish foreign ministry's first travel advisory warned of "dangerous levels of religious intolerance and hatred in Europe".

A separate statement said "there have recently been verbal and physical attacks against foreigners and acts of racism committed throughout the United States."

Finland and Sweden broke with decades of military non-alignment and applied to join NATO in response to Russia's invasion of Ukraine.

Bids to join NATO must be approved by all 30 members of the alliance.

Turkey and Hungary are the only members not to have ratified the two applications by votes in parliament.

Hungary's legislature is expected to ratify the two bids next month.

But Turkish President Recep Tayyip Erdogan has dug in his heels heading into a May 14 presidential election in which he is trying to energise his nationalist base.