The breakthrough came after four hours of talks just before a NATO summit began in Madrid, averting an embarrassing impasse at the gathering of 30 leaders that aims to show resolve against Russia, now seen by the U.S.-led alliance as a direct security threat rather than a possible adversary.

It means Helsinki and Stockholm can proceed with their application to join the nuclear-armed alliance, cementing what is set to be the biggest shift in European security in decades, as the two, long-neutral Nordic countries seek NATO protection.

Turkey’s main demands, which came as a surprise to NATO allies in late May, were for the Nordic countries to stop supporting Kurdish militant groups present on their territory, and to lift their bans on some sales of arms to Turkey.

The country has raised serious concerns that Sweden has been harboring what it says are militants from the banned Kurdistan Workers Party (PKK), which took up arms against the Turkish state in 1984. Stockholm denies the accusation.

Turkey had opposed their bids over what it called support for Kurdish militants and others it views as terrorists, as well as over arms embargoes and unfulfilled extradition requests. It demanded binding promises and concrete steps to lift its veto.

After hours-long negotiations between their leaders and NATO in Madrid, the three nations signed a deal for Ankara to remove its block, while the candidates pledged not to support the Kurdish militant PKK and YPG groups.

The Kurdish YPG militia is a key part of the SDF that controls large parts of northern Syria and is regarded by Washington as an important ally against the Islamic State. Ankara sees it as an extension of the militant PKK, branding it a terrorist group, while Western governments do not.

Reporter's code: 50101