Willie Walsh said an assessment from the International Energy Agency that fuel for aircraft could start running out in Europe in six weeks' time was "sobering".

"We have also estimated that by the end of May we could start to see some cancellations in Europe for lack of jet fuel. This is already happening in parts of Asia," he said in a statement.

The projected aviation fuel shortage stemmed from Iran's effective blockage of the Strait of Hormuz since the United States and Israel started the war at the end of February which spread across the Middle East.

Although Iran's foreign minister said on Friday his country was now reopening the strait to commercial traffic, shipping companies are wary.

Walsh said in his statement issued before Iran's announcement that, if jet fuel shortages occurred, "it's important that authorities have well-communicated and well-coordinated plans in place in case rationing becomes necessary."

The EU's energy commissioner Dan Jorgensen told the Financial Times that the fuel threat meant that flights could soon be cancelled. He suggested EU countries might share jet fuel to cushion the impact in case of a lengthy crisis.

An EU spokeswoman, Anna-Kaisa Itkonen, told journalists that, at this moment, "there is no indication of a systemic fuel shortages that would lead to widespread flight cancellations".