U.K. airlines and cruise ships resumed flights on Tuesday after a U.N. panel ordered them to resume after their passengers reported feeling ill, but the U.A.E. warned the outbreak was not over and the country could be forced to return to its isolation protocols.

British Airways said its Airbus A320-200 planes had been grounded while it investigated a report of an “unexpected and potentially life-threatening” illness on board.

It said a passenger had reported “unusual symptoms” and a flight to London was cancelled.

British officials did not immediately provide details on what the passenger had been diagnosed with or how he or she got ill.

British Foreign Secretary Philip Hammond told reporters that Britain would continue to look into the “potential” of the case, which was not being treated as a terrorist incident.

“We have had no reports of any terrorist incidents so far and I would urge the British public to remain vigilant in their travel,” he said.

Hammond said that Britain was “still assessing the situation and we would do everything possible to minimise any disruption to flights, especially in the coming days and weeks.”

He said Britain was working closely with the U-N.

to ensure that the issue was dealt with swiftly.

“The UK Government has worked closely with our international partners in a very robust and constructive way,” Hammond said.

The U.G. is expected to issue its own travel advisory soon.