Evidence now suggests that a bomb planted by the Islamic State militant group is the likely cause of last weekend’s crash of a Russian airliner over Egypt’s Sinai peninsula, U.S. and European security sources said on Wednesday, reports.

Islamic State, which controls swathes of Iraq and Syria and is battling the Egyptian army in the Sinai Peninsula, said again on Wednesday it brought down the airplane, adding it would eventually tell the world how it carried out the attack.

The Airbus A321 crashed on Saturday in the Sinai Peninsula shortly after taking off from the resort of Sharm el-Sheikh on its way to the Russian city of St Petersburg, killing all 224 people on board.

The U.S. and European security sources stressed they had reached no final conclusions about the crash.

Britain on Wednesday cited the likely possibility of an explosive device as the cause of the crash, but made no mention of any group that may have been responsible.

“We have concluded that there is a significant possibility that the crash was caused by an explosive device on board the aircraft,” Britain’s foreign secretary, Philip Hammond, said after a meeting of the government’s crisis response committee chaired by Prime Minister David Cameron.