Malaysia Airlines re-routed a Kuala Lumpur-to-London flight over Syrian airspace yesterday after its usual route over Ukraine was closed, flight tracking data showed.

Flightradar24 posted a flight map on its Twitter account today showing the change in the flight's route.

Flight tracking data showed this flight had previously crossed over eastern Ukraine.

After Malaysia Airlines Flight MH17 was shot down last Thursday by a ground-to-air missile in eastern Ukraine, airlines began to avoid the airspace above where the Ukrainian military has been fighting Russian-backed rebels.

On Friday and Saturday the Kuala Lumpur-London flight, MH4, had taken a different route over eastern Turkey, tracking data showed.

The change in route on Sunday highlighted the challenge that airlines face in finding conflict-free passageways on congested routes between Asia and Europe.

Hundreds of flights routinely crossed over Ukraine before Thursday's incident, and it is not unusual for international airlines to overfly war zones such as Syria or Afghanistan.

The US Federal Aviation Administration, whose regulations are among the world's strictest, "strongly discourages" US operators from flying to, from or over Syria, according to a May 2013 notice on its website.

Malaysia Airlines said the MH4's flight plan was in accordance with the International Civil Aviation Organization's (ICAO) approved routes.

"As per the notice to airmen (NOTAM) issued by the Syrian Civil Aviation Authority, the Syrian airspace was not subject to restrictions," Malaysia Airlines said in a statement.

"At all times, MH4 was in airspace approved by ICAO."