The probe into the disappearance of a Malaysia Airlines plane does not yet include the FBI. 

A senior U.S. law enforcement official says representatives from other agencies and Boeing are expected to arrive in Kuala Lumpur on Monday. 

Malaysia Airlines flight 370 disappeared suddenly from radar screens Saturday en route to Beijing. There were 239 passengers and crew aboard the Boeing 777.  

The FBI has offered to help in the investigation. Officials investigating the disappearance of the jet think it may have disintegrated in mid-flight. 

Officials say had the jet plunged into the water from such a height, search teams would have expected to locate a fairly concentrated pattern of debris. 

Meanwhile, Vietnam's ministry of information says a search aircraft has located fragments floating in the waters off southern Vietnam that are thought to be part of the Malaysia Airlines jetliner that went missing. 

More than 30 aircraft and 40 ships are searching for any sign of the plane. Two-hundred-thirty-nine passengers and crew are feared lost.  

An investigation continues into reports that four passengers used stolen passports to board the aircraft. Republican Representative Mike Rogers of Michigan chairs the House Intelligence Committee. He told ABC's "This Week" it's not uncommon. Rogers says the the reason for this is mainly the quality of the passports themselves.