Nato on Wednesday declined an overture by Qatar to join the Western military defence alliance, saying membership was reserved to the United States and Europe.
It was responding to a comment by Qatar's defence minister on Tuesday that his country's long-term strategic "ambition" was to join Nato.
"According to Article 10 of the Washington Treaty, only European countries can become members of Nato," an official of the 29-country alliance told AFP.
"Qatar is a valuable and longstanding partner of Nato," the official said.
Speaking on the anniversary of a bitter year-long diplomatic dispute among Gulf nations that has seen Qatar isolated from its former regional allies, Defence Minister Khalid bin Mohamed Al-Attiyah said Qatar wanted to become a full member of Nato.
"Qatar today has become one of the most important countries in the region in terms of the quality of armament," Attiyah told the official magazine of the Qatari defence ministry, Altalaya.
"Regarding the membership, we are a main ally from outside Nato... The ambition is full membership if our partnership with Nato develops and our vision is clear."
His remarks come at a politically sensitive time in the region.
On June 5, 2017, Saudi Arabia the United Arab Emirates, Bahrain and Egypt abruptly severed ties with Qatar, accusing it of supporting terrorism and Iran.
The four countries expelled Qataris, and the country's only land border with Saudi Arabia has been closed for the past year.
Diplomatic efforts have so far proved fruitless in what was previously one of the most stable regions in the Arab world.