A flag flies at half mast at the State Duma in Moscow, Nov 1, 2015, to mourn the victims aboard the Russian plane that crashed Saturday in Egypt's Sinai.[Photo/Xinhua]

WASHINGTON - The White House said Thursday that the United States cannot rule out the possibility of "terrorist involvement" in the downing of a Russian passenger jet in Egypt that killed all 224 people onboard.

"At this point we've not made our own determination about what exactly led to this tragic incident," White House spokesman Josh Earnest said at a press briefing. "But at the same time we can't rule anything out, including the possibility of terrorist involvement."

The Airbus A321 operated by Russia's airline Kogalymavia crashed early Saturday in the Sinai Peninsula shortly after taking off from Egypt's Red Sea resort Sharm el-Sheikh.

US Cable News Network (CNN) reported Wednesday that the latest US intelligence suggested that the crash of the plane in Egypt was most likely caused by a bomb planted by the terror group Islamic State (IS) or its affiliate.

"There is a definite feeling it was an explosive device planted in luggage or somewhere on the plane," CNN quoted a US official as saying.

But the official added that there has not been a formal conclusion reached by the US intelligence community on the cause of the crash.

Sinai Province, a militant Egyptian group affiliated with the IS, claimed responsibility for Saturday's downing of the Russian plane through a statement. The group has been active in Sinai fighting with Egyptian security forces.

But the claim has not been verified by Egyptian or Russian officials.