LONDON - Jordan has asked all airlines landing at its airports to carry 45 minutes of reserve fuel, in what experts see as a precautionary measure in case of an attack by Iran against Israel.

Some airlines are already avoiding Iranian and Lebanese airspace and cancelling flights to Israel and Lebanon, as concerns grow over a possible conflict in the region after the killing of senior members of militant groups Hamas and Hezbollah last week.

The NOTAM, a safety notice provided to pilots, was issued on Sunday by Jordanian authorities, asking all airlines to carry the reserve fuel for "operational reasons". It is effective until 2200 GMT on Tuesday.

In a bulletin, OPSGROUP, a membership-based organisation that shares flight risk information, said the move was ahead of the anticipated closure of Jordanian airspace, a cautionary move in case of an attack on Israel by Iran.

"The Jordan NOTAM is relevant because in the April aerial attack on Israel, Jordan was the first country to close their airspace by NOTAM, well ahead of even Israel, Iran, or Iraq," Mark Zee, OPSGROUP's Chief Executive, told Reuters.

"The 45 minutes would be intended to provide enough additional fuel for an aircraft to leave Jordanian airspace and land elsewhere," he added.

Airspace closures tied to war can place substantial restrictions on air traffic.

The war in Ukraine, for example, has placed significant constraints on European airspace, already under pressure from air traffic control strikes and strong travel demand.

In the Middle East, experts say the impact could be even bigger.

"An attack by Iran on Israel would result in the closure of some of the most heavily trafficked air routes in the world," said Ian Petchenik, spokesperson for flight tracker FlightRadar24.

"Closure of this airspace will force aircraft into ever-narrowing corridors to the north and south. Any sustained closure of these routes would be a monumental reordering of international air traffic."

(Reporting by Joanna Plucinska; Editing by Christina Fincher)