“Is believed to,” “is thought to,” “is understood to” are agentless passives: they state a belief while surgically removing the believer. That deletion is the trick — it floats an unverified claim free of any source, as if the belief were just in the air.

The holder might be the intelligence community, one official, or the reporter’s own read. Said plainly, the sentence would have to name a believer and their basis; in the passive, it names neither.