ISTANBUL — The United Arab Emirates said Monday that two of its civilian airliners were "intercepted" by a fighter jet from Qatar during routine flights, in a sign of rapidly escalating tensions between the quarreling Persian Gulf neighbors.

It was not immediately clear what was meant by "intercepted." A spokeswoman for Qatar's Ministry of Foreign Affairs dismissed the reports as "baseless." 

The accusation comes against the backdrop of Qatar's own claims of interference by the UAE. In recent weeks, Qatar has accused the fellow gulf country of violating its airspace twice with military flights, raising concerns that their lengthy but low-intensity feud could soon escalate into an armed confrontation.  

The two countries broke off diplomatic relations in June, when the UAE, Saudi Arabia and two other Arab states severed air, land and sea links with Qatar. The Arab bloc accused Qatar of supporting Iran and terrorist groups. Qatar denied the accusations and said it was being punished for pursuing regional policies independent of Saudi Arabia and its allies.

The feud has divided the Trump administration's closest regional partners, jumbled alliances across the Middle East and radiated insults and accusations that recall a schoolyard brawl. The quarrel has contributed to an extraordinary period of turbulence across the gulf, exacerbated by the nearly three-year-old civil war in Yemen, as well as the ongoing and bitter rivalry between Saudi Arabia and Iran.  

For months after the initial break in diplomatic relations, Kuwaiti and Western officials tried in vain to broker a settlement, even as Qatar and its adversaries enlisted lobbyists and public relations firms to argue their claims in Washington and other foreign capitals.  

A White House statement, summarizing a call Monday between President Trump and Qatar's emir, Tamim bin Hamad al-Thani, made no mention of the airline incident. Trump thanked the emir for "Qatari action to counter terrorism and extremism in all forms, including being one of the few countries to move forward on a bilateral memorandum of understanding" — a reference to an agreement signed in July between the United States and Qatar to combat terrorism and its financing.

Statements on Monday by the UAE's General Civil Aviation Authority called the interceptions of the civilian airliners, which were traveling to Bahrain, a "clear violation of international law." The statements did not name the carrier or say exactly where the incident occurred. Qatari warplanes were detected by radar in Bahrain and were seen by crew members and passengers on the airliners, the state-run Emirates News Agency said.  

U.S. Air Force 2nd Lt. Jenna Lenski, a spokeswoman based at the Combined Air Operations Center at the Al Udeid Air Base in Qatar, referred questions about the incident to the Qatari Defense Ministry. 

But Qatar asserted that the UAE had fabricated the reports to divert attention from its own recent violations of Qatar's airspace. A lengthy statement by Qatar's foreign ministry Monday noted that the accusations came three days after Qatar notified the United Nations of UAE violations, which it said occurred Dec. 21 and Jan. 3.  

Another incursion into Qatari airspace — by a UAE C-130 — occurred Sunday, the statement said.  

The dueling accusations over airspace were not the only signs that the gulf feud was worsening. On Sunday, in a bizarre turn, a member of Qatar's ruling family appeared in an online video, claiming that he was being detained in the UAE. The ruling family member, Sheikh Abdullah bin Ali al-Thani, had previously been hosted and promoted by members of a Saudi-led bloc, suggesting that they viewed him as an alternative to the current Qatari leadership.

The video followed similarly strange incidents involving coercion in the gulf states, including the apparently forced resignation of Lebanon's prime minister during a visit to Saudi Arabia and claims by an Egyptian political figure in November that the UAE had temporarily prevented him from leaving the country. 

The UAE denied that Thani was being detained, calling him a "guest" who had "unrestrained mobility," according to a Foreign Ministry statement.