Thaksin Shinawatra set off for Finland on a foreign tour on September 9, loading up his government-assigned aircraft with 58 large suitcases and trunks, an official from Thai Airways International said on Sunday on condition of anonymity.
The prime minister's aircraft, named Thai Koofah, was then left parked in Finland for more than a week as Thaksin continued his trip on other transportation.
Another aircraft carrying 56 suitcases - an Airbus 340-600 - was dispatched from Bangkok to meet the prime minister just days before the coup, the official from the national carrier said.
The official said it was not known what was taken aboard the second aircraft because only Thaksin's aides were allowed to supervise the loading.
"I want the [military] council to investigate this because we, the employees of Thai Airways International, believe that Thaksin exploited the company through his power as prime minister by using a company airplane to transport his assets out of the country," the airline official said.
A second official in the airline industry confirmed that the second flight left on September 17, two days before Thaksin was toppled in a coup.
It was unclear why Thaksin needed the second aircraft when his own plane had already been assigned to fly him to Europe and the US.
When asked about Thaksin taking his assets abroad, Lieutenant General Palanggoon Klaharn, the ruling military council spokesman, said: "No comment. I can't comment on that".
Thailand's new ruling military council has said it will start an investigation into alleged wrongdoing under Thaksin's government, which critics say was riddled with corruption and abuse of power.
A spokeswoman for the airline said she was not aware of the incident "and even if it is true, Thai Airways would only report it to the [council], not to the media'.
The military council took power in
a bloodless coup on Tuesday
Earlier, one of Thaksin's opponents, publishing tycoon Sondhi Limthongkul, alleged that the former leader had chartered two Russian aircraft to take some of his assets out of Thailand.
Sondhi, one of the leaders of mass street demonstrations against Thaksin earlier this year, made the allegations on his weekly television programme a week before the former prime minister departed for Finland and repeated them the following week.
Thaksin's family is among the wealthiest in Thailand, and in 2004 the Forbes magazine ranked Thaksin as the 16th richest man in Southeast Asia.
In January, the then-prime minister sold part of his empire - telecoms giant Shin Corp - to Singapore's state investment company, Temasek Holdings, for a tax-free 73.3 billion baht ($1.9 billion).
Pridiyathorn Devakul, the head of the country's central bank, had said the proceeds from the sale were probably still in Thailand.
"I estimate that no large amount of Thai baht has been converted into overseas currencies. However, I don't now whether the money could have been packed in suitcases and taken abroad," he said last week.
Thaksin and one of his children have been in London since the coup, while his wife and two other children remain in Thailand.