Late on Sunday, Vietnamese authorities said that they had identified two objects in the water about 90 kilometers (55 miles) south of Vietnam's Tho Chu island.

State media speculated that the object could be a part of the Malaysian Airlines jet that went missing en route from Kuala Lumpur to Beijing.

"We received information from a Vietnamese plane saying that they found two broken objects, which seem like those of an aircraft, located about 50 miles to the southwest of Tho Chu Island," a senior official from Vietnam's national search and rescue committee told the AFP news agency.

Planes and boats were to be sent to the area to investigate on Monday, the official said. "As it is night they (the objects) cannot fish them out for proper identification. They have located the position of the areas and flown back to the land," the official said.

There was also a report from the deputy chief of staff of the Vietnamese army that an object thought to be a door had been spotted.

Malaysian officials had earlier said that no traces of the aircraft, a Boeing 777 jetliner, had been found. However, late on Saturday, two large oil slicks were detected off Tho Chu, part of a tiny archipelago off the southwestern tip of Vietnam.

The plane went missing early Saturday morning, two hours after taking off from the Malaysian capital for Beijing, never having made it to China.

Investigators seek explanation

Early investigations have thrown up the possibility that the plane disintegrated while in the air, the pilots being unable or having too little time to send a distress signal.

Malaysia's air force chief, Rodzali Daud, also said on Sunday that there was some evidence tat the plane may have turned back, with the search being expanded. "We are trying to make sense of this" he told a news conference. "The military radar indicated that the aircraft may have made a turn back and, in some parts, this was corroborated by civilian radar."

Meanwhile, Interpol announced that it was investigating suspect passports in addition to two European ones that were used by unidentified passengers. Authorities have confirmed that the passports of an Austrian and Italian who were initially thought to be on the plane had been stolen in Thailand within the last two years.

An Interpol spokeswoman said a check of all documents used to board the plane had revealed more suspicious passports, but did not give details about the countries they came from.

rc/mkg (AP, AFP, dpa, Reuters)