WASHINGTON — With malicious intent strongly suspected in the disappearance of Malaysia Airlines Flight 370, American intelligence and law enforcement agencies renewed their search over the weekend for any evidence that the plane’s diversion was part of a terrorist plot. But they have found nothing so far, senior officials said, and their efforts have been limited by the Malaysian authorities’ refusal to accept large-scale American assistance.

There are just two F.B.I. agents in Kuala Lumpur, the Malaysian capital, where local investigators are hunting for clues that the two pilots or any of the other 237 people on board had links to militant groups or other motives to hijack the flight.

In the days after the plane went missing on March 8, American investigators scoured their huge intelligence databases for information about those on board but came up dry.

“We just don’t have the right to just take over the investigation,” said a senior American official who, like others, spoke on the condition of anonymity because the investigation was continuing. “There’s not a whole lot we can do absent of a request from them for more help or a development that relates to information we may have.”