Turkish President Recep Tayyip Erdoğan hinted at an interest in acquiring nuclear weapons, telling the United Nations that it is unjust for the weapons to be possessed only by major powers.

“It bothers us like anyone else that the weapons of mass destruction are used as leverage in every crisis instead of their total elimination,” Erdoğan said Tuesday during the annual meeting of the U.N. General Assembly in New York. “The position of nuclear power should either be forbidden for all or permissible for everyone.”

Erdoğan’s comments punctuated a complaint about the influence wielded in international affairs by the five permanent members of the United Nations Security Council. His remarks, an implicit challenge to the Nuclear Non-Proliferation Treaty that Turkey signed in 1980, could signal additional friction with the President Trump over Iran’s nuclear weapons program and the NATO ally’s willingness to remain sheltered under the United States nuclear umbrella.

“The world is greater than five,” Erdoğan said. “It is nigh time that we change our current mentality, our institutions, organizations, and rules.”

That’s a reference to the five countries — the United States, China, France, Russia, and the United Kingdom — that have the ability to veto a resolution at in the U.N. Security Council. Those same five countries are recognized as nuclear powers under the NPT, a treaty that took force in 1970 and now has a total of 191 signatories.

“He seems to have upgraded his challenge by bringing in the nuclear weapons issue,” Foundation for Defense of Democracies senior fellow Aykan Erdemir, a former member of the Turkish parliament, told the Washington Examiner. “At this point, his call for nuclear weapons is for the most part an empty rhetoric, geared more to boost his popularity at home. Since Erdoğan can’t deliver on the economic front, he has to cater to the electorate’s nationalist sentiment by hinting at the possibility of a nuclear Turkey.”

He made the hints more explicitly at a lower-profile forum earlier this month. I cannot possess missiles with nuclear warheads? I do not accept that," Erdoğan said at the Central Anatolian Economic Forum in Turkey.

U.S. relations with Turkey, a key member of NATO, are already strained by a series of disagreements. Erdoğan believes the U.S., in an attempt to defeat the Islamic State in Syria and Iraq, partnered with Kurdish terrorists hostile to the Turkish government. And Turkey’s determination to purchase an advanced anti-aircraft missile system from Russia drove the Trump administration to deny Turkey access to the U.S.-made F-35 stealth fighter jet.

Erdoğan delivered his speech shortly after Trump called for world powers to prevent Iran, whose leaders in Tehran enjoy warming relations with Turkey, from obtaining nuclear weapons.

“Not only is Iran the world’s number one state-sponsor of terrorism, but Iran’s leaders are fueling the tragic wars in both Syria and Yemen,” Trump told the General Assembly. “At the same time the regime is squandering the nations wealth and future in a fanatical quest for nuclear weapons and the means to deliver them. We must never allow this to happen.”

But Erdoğan maintained that it is the current nuclear powers who are driving such controversies.

“The inequality between nuclear states and non-nuclear states is alone enough to undermine global balances,” he said.