A statement said the slicks, each between 10km and 15km long, and 500m apart, were spotted some 140m south of Tho Chu island off southern Vietnam.
The statement said the slicks were consistent with the kind that would be left by fuel from a crashed jetliner.
The Boeing 777-222 jet disappeared from radar screens with 239 people on board en route to Beijing after taking off from KL International Airport at 12.41am.
It went off the radar screen at 1.30am.
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