The United Arab Emirates said on Monday Qatari air force jets had twice intercepted its civilian aircraft during routine flights to Bahrain, but Qatar called the claim "completely untrue."
Qatar said the allegation, reported by the UAE's state news agency WAM, was intended to divert attention from what it said were violations by Emirati military aircraft of its airspace.
The UAE is one of four Arab countries, along with Saudi Arabia, Bahrain and Egypt, that imposed travel, diplomatic and trade sanctions on Qatar in June 2017, accusing it of supporting terrorism.
Qatar has denied the charges and accused the four countries of trying to make it conform to their foreign policy positions.
Qatar's rivals have banned Qatari aircraft from their airspace but Doha has not reciprocated with a ban of its own.
The UAE General Civil Aviation Authority said two Emirati airliners, carrying 277 passengers, had encountered the jets from Qatar, which lies between the UAE and Bahrain, while en route to Bahrain, according to WAM.
One of the planes was intercepted at 10:30 a.m., and the second at 11:05 a.m. at between 9,000 and 10,000 feet. The report did not specify a date, but appeared to mean the incidents happened on Monday.
"Bahraini radars have tracked the Qatari military planes while intercepting the Emirati civilian aircraft," WAM quoted civil aviation director Saif al-Suwaidi as saying.
"The incident could also be seen by the naked eye by both the crew and passengers, which constitutes a clear threat to the lives of innocent civilians," he added.
The UAE condemned the Qatari action as "a serious and renewed breach of international conventions and the safety of civil aircraft traffic."
The UAE Civil Aviation Authority did not say which airlines were involved, but Bahrain's state news agency BNA said the first flight was from Emirates. The airline is owned by the government of Dubai, one of seven emirates in the UAE federation. It gave no details of the second flight.
Qatar's foreign ministry said the UAE allegation followed incidents on December 21 and January 3 in which UAE military aircraft had violated its airspace.
Ministry spokeswoman Lulwa Rashed al-Khater said Qatar planned to take legal action against the UAE over the incidents.
"It seems that the Civil Aviation Authority in the UAE, by publishing false claims, is trying to pre-empt events and cover over news of the Emirati plane penetration of Qatari airspace," Khater said in the statement, posted on the ministry's website.
On Friday, Qatar said it had filed a complaint with the United Nations about the alleged violation of its airspace on December 21. The UAE denied the allegation.
Reporting by Noah Browning, Aziz el Yaakoubi, Mohamed el Sherif and Mostafa Hashem; editing by Andrew Roche.