"The announcement that US President Trump will attend the summit in person is a significant step in terms of the alliance's stability," the Turkish leader told lawmakers from his ruling AKP party.

Last week, US Secretary of State Marco Rubio confirmed Trump would attend the July 7-8 summit in the Turkish capital, as concerns linger about Washington's commitment to the transatlantic alliance.

"We're still in NATO, but NATO needs significant changes," Rubio told US lawmakers, describing the summit of the 32 member states as "probably the most important meeting in NATO's history".

Erdogan said Turkey had intensified its preparations "to ensure the Ankara summit becomes a landmark in NATO's history".

Relations within the alliance have been put under significant strain since the United States and Israel began bombing Iran on February 28.

European governments declined to join the war, which was also opposed by Turkey, with Ankara working hard towards efforts to end to the fighting.

Rubio also expressed frustration over Spain's refusal to let US forces use its bases for strikes on Iran.

"We have members of that alliance that are basically denying the use of those bases," Rubio complained, saying it was cause "to question the entire thing".