The Sun newspaper on Thursday quoted an unnamed senior Royal Air Force source as saying that a bomb planted by Iraqi fighters most likely caused the C-130 Hercules plane to crash in Iraq on 30 January, killing 10 servicemen.
"A bomb now looks the most likely cause of the crash," the source said.
The newspaper reported that investigators thought it was unlikely the plane suffered a mechanical problem, or was hit by a surface-to-air missile, or that ammunition on board the aircraft exploded.
The entire right wing of the plane was torn off, sending the plane instantly into a violent spin and causing it to break up in four seconds.
Investigators say ammunition or a missile would not have caused the wing to sheer off. The aircraft was probably also out of missile range.
"But sabotage is another distinct possibility. Metal fatigue is another option but is considered much less likely. The suggestion that the plane was hit by a missile is a virtual non-starter"
Unnamed Royal Air Force source
"But sabotage is another distinct possibility. Metal fatigue is another option but is considered much less likely. The suggestion that the plane was hit by a missile is a virtual non-starter," the source said.
Meanwhile, a senior US general said he believed the crash was due to an attack rather than a technical problem.
"I personally believe that there may have been hostile action or something that happened inside the aircraft, but I don't think it was mechanical in nature," said Lieutenant-General Lance Smith, deputy commander of the US Central Command in Iraq.
The crash resulted in Britain's largest single-day loss of life since the US-led invasion of Iraq in March 2003.