New evidence indicates the Russian plane that crashed in the Sinai Peninsula on Saturday may have been brought down by a bomb or explosive device.

A U.S. official told NBC News on Wednesday that Islamic State operatives or affiliates were likely responsible for causing the crash of Metrojet Flight 9268. All 224 people onboard were killed in the disaster.

Investigators are looking at the possibility that an explosive was smuggled onto the plane by ground crew or baggage handlers at the Sharm el-Sheikh airport.

An Egyptian source close to the investigation confirmed the claims to Reuters.

"It is believed to be an explosion but what kind is not clear. There is an examination of the sand at the crash site to try and determine if it was a bomb," said the source. "There are forensic investigations underway at the crash site. That will help determine the cause, to see if traces of explosives are found."

Terrorist activity was suspected earlier in the week, after an unspecified group of ISIS sympathizers took the blame for the crash via social media.

According to a U.S. official, the passenger manifest and flight crew held no one with any known terrorist affiliations.

The Guardian reports the British government has made the decision to suspend all flights from the UK to the Egyptian resort of Sharm el-Sheikh, advising against all but essential air travel.

"That means there will be no UK passenger flights out to Sharm el-Sheikh from now. Passengers on the ground in Sharm el-Sheikh will be returned to the UK," said foreign secretary, Phillip Hammond. "We are working with the airlines and the Egyptian authorities to put in place emergency procedures for additional screening and additional security to make sure they can get home safely either on the original dates or if they wish to leave earlier on an earlier date."

There are an estimated 20,000 British citizens currently on holiday at Sharm el-Sheikh.

No U.S. commercial flights operate over Sinai. Nevertheless, State Department spokesman John Kirby told reporters that U.S. workers should also avoid traveling to the region.