The UAE’s aviation authority said that Qatari fighter jets intercepted two commercial planes operated by national carriers on Monday during routine flights to the Bahraini capital Manama.

The General Civil Aviation Authority (GCAA) said the first flight was on a regular scheduled trip on Monday morning with all necessary permits and approvals when it was “intercepted by Qatari fighters”, according to state news agency WAM.

It described the incident as a “flagrant and serious threat to the safety of civil aviation” and in “clear violation of international laws and conventions”.

Bahrain’s foreign ministry identified the intercepted plane as Emirates flight 837 in a statement strongly condemning the “hostile behaviour by Qatar against civil aircraft” that “has become frequent in recent times”.

The ministry added that it supported any measures taken by the UAE in response to the incident that posed a “threat to the lives of civilians”.

Later on Monday afternoon, the UAE aviation regulator said a second scheduled flight was also intercepted on its way to Bahrain International Airport.

Etihad was identified as the carrier operating the flight by Bahrain. The two planes were carrying 277 passengers in total, according to the UAE authority.

The General Civil Aviation Authority said it was reviewing its legal options via United Nations agency the International Civil Aviation Organisation.

Saif Al Suwaidi, director general of the GCAA, said in a later statement Qatar had shown no prior objection to the path used by the two aircraft and the fighter interception was seen by crew and passengers on board the planes proving it “posed a present and clear threat to the lives of innocent civilians”.

“The Qatari fighter jets intercepted the first plane at 10:30am, while the second was intercepted at 11:05am while flying at 9,000 to 10,000 feet altitude in regular flights approved by the International Civil Aviation Organisation, ICAO,” he added.

Qatar’s Foreign Ministry described the allegations as a “totally false claim” in a statement issued on Monday night.

Qatar had previously accused UAE fighter jets of violating its airspace on two previous occasions.

Ties between the UAE and Qatar have been strained since the emirates joined a Saudi-led boycott of the country last June.

Saudi Arabia, the UAE and Bahrain have closed air, sea and land links to Qatar and prevented Qatari aircraft from using their respective airspace.

Tensions increased on Sunday when Qatari media carried a video purported to show royal Sheikh Abdullah bin Ali al-Thani saying he was being detained in Abu Dhabi against his will.

The UAE denied the claims and said Sheikh Abdullah, who had emerged as a potential opposition figure after the row over Qatar erupted last June, had left the country.

“It seems that the UAE is trying to draw attention away from other incidents that have caused media crises,” the Qatar Foreign Ministry said in an apparent reference to the video.

Read: UAE says Qatari royal leaves after claim he was being detained