It said more than 600 hastily buried bodies would have to be exhumed for fuller forensic tests. More than 2000 of the country's 5303 known dead have yet to be identified.
Even the most basic identification of many corpses as Thai or foreigner needed to be checked again, officials said on Monday.
A senior official at the national disaster centre on Phuket island said the identification of the race of a dead person was often done only visually.
"From now on, when we say we can identify them, we must know their names and have some sort of document to verify their identification," said the official.
Early in the day, the flow of aid in Indonesia was forced to pause after a US helicopter crash and a powerful tremor on northern Sumatra island.
Panic-stricken people in the devastated Indonesian city of Banda Aceh fled homes and shelters after a pre-dawn aftershock.
More than 2000 bodies have yet
to be identified in Thailand
And with hope all but gone of finding anyone alive among the tens of thousands of missing, a cargo ship picked up an Indonesian survivor adrift in the Indian Ocean - the third person to be rescued that way - and was steaming towards Malaysia.
Meanwhile, the global response to the disaster has seen governments and agencies pledge more than $5 billion in aid while companies and individuals have promised $1.5 billion.
In Australia, more than 70,000 fans packed Melbourne Cricket Ground for a tsunami charity match featuring some of the world's top players that raised A$14 million ($11 million).
The World Food Programme said it was optimistic no survivors would lose their lives to hunger, and aid should reach nearly all of them within a week.
It said it had doubled to 300,000 the number of people to whom it was distributing food in Aceh.
Banda Aceh revives
Tonnes of food, medicine, tents and drinking water are being flown to Banda Aceh in a stream of aircraft. A ghost town after the tsunami, the city has revived as hundreds return to pick through what remains of their homes and businesses.
While thousands live in makeshift camps, residents not affected are renting out homes for $5000 a month or more to the hundreds of aid workers flowing in.
The tsunami triggered by the 9.0-magnitude quake killed at least 156,000 people around the Indian Ocean, with Aceh province on Sumatra's northern tip accounting for almost all of Indonesia's 104,000 deaths.
The waves killed about 30,000 people in Sri Lanka, 15,000 in India, more than 5000 in Thailand and others in the Maldives, Myanmar and some east African nations.