UPDATE, 7:15 p.m.: Freescale Semiconductor, a company based in Texas, confirms 20 of its employees — 12 from Malaysia and eight from China — were passengers on missing Malaysia Airlines flight en route from Kuala Lumpur to Beijing.

LATEST: Officials Say Oil Slicks Not From Missing Malaysia Airlines Flight

A U.S. official tells Fox News that the priority in investigating the disappearance of a Malaysia Airlines jet is determining the status of two passports previously reported stolen that were used to gain access to the flight, and who boarded the plane under those names.

Italy’s Foreign Ministry said Luigi Maraldi was listed aboard the flight. He reported his passport stolen last August.  The Austrian Foreign Ministry said that an unnamed man listed on the manifest matched an Austrian passport that was reported stolen two years ago. He was not on the plane.

Malaysia Airlines Boeing 777 was carrying 239 people, including two infants, when it fell off the radar. It "lost all contact and radar signal one minute before it entered Vietnam's air traffic control," Lt. Gen. Vo Van Tuan, deputy chief of staff of the Vietnamese army, said in a statement.

Search Underway for Missing Malaysia Airlines Flight Carrying 239 People

Two oil slicks, measuring between 6 and 9 miles long, have been spotted. There has been no official confirmation that these are related to the missing plane, but a statement from the Vietnamese government said they were consistent with the oil slicks of a crashed jetliner.

There have been no signs of wreckage yet.

“If it was a bomb or an explosion, it would be debris spread over a large area […] If it just went down in a straight dive, which is very perplexing, you would probably not have it, and that may be the oil slick,” Fox News contributor Lt. Gen. Tom McInerney said.

Authorities have not ruled out terrorism.