A massive search and rescue operation enters its fourth day for a missing Malaysia Airlines jetliner.

Ships and aircraft from 10 countries scour the waters off Malaysia and Vietnam but none of the debris or oil slicks spotted earlier has proved to be linked to the disappearance.

. (SOUNDBITE) (English) DIRECTOR GENERAL FOR DEPARTMENT OF CIVIL AVIATION, AZHARUDDIN ABDUL RAHMAN, SAYING:

"On the oil slick that was found by the maritime enforcement agency of Malaysia, they have sent the samples to the chemistry department today and we have got the report from the chemistry department of Malaysia, they have reported that, they have confirmed that the oil are not from an aircraft."

Malaysia's civil aviation chief said the search area has been doubled since flight MH370 vanished on Saturday shortly after it left Kuala Lumpur.

The focus has been on two passengers who boarded the flight using stolen European passports.

(SOUNDBITE) (English) DIRECTOR GENERAL