The protests, by disgruntled supporters of self-exiled Thaksin, descended into Thailand's worst political violence in living memory when troops moved in to disperse them on May 19.

The government has launched a reconciliation plan aimed at healing divisions between Thaksin's rural and urban poor supporters and the military and royalist-linked establishment.

But it has also blamed Thaksin and allies for instigating the violence and filed charges of terrorism against them.

The Department of Special Investigation (DSI) — Thailand's equivalent of the US FBI — said 69 individuals and 14 companies made unusually large and frequent financial transactions beginning in September 2009 and running through two months of protests that troops forcibly ended last month.

"This is not an arrest or an indictment," Tharit Pengdith, the director general of the DSI, told reporters, referring to a list of people the authorities want to question, which includes Thaksin, his former wife, their two children, and many allies.

Authorities will summon these individuals to explain their transactions by July 31, Tharit said. He offered no evidence of how the transactions may have been linked to the unrest.

"We have no evidence beyond the fact that the transactions were unusually large and frequent, so we are asking these individuals to explain what the transactions were for, to establish whether they were linked to the protest," he said.

Thaksin, a telecoms tycoon turned populist politician, was ousted in a 2006 military coup and later convicted of graft.

He is widely believed to have funded anti-government protests in recent years but has denied such accusations, including the funding of groups the government has called "shadowy militants,” some of whom were armed with rifles and grenades and battled security forces during the most recent protest in Bangkok.

The violence, in which 90 people were killed and about 2,000 wounded, scared off tourists and hurt growth, although recent data showed Southeast Asia's second-biggest economy remained buoyant.

The stock market has recovered from losses suffered during the turmoil, although foreign investors remain cautious.

In an example of the sort of financial transactions investigators were looking into, the DSI said 4.23 billion baht ($130 million) was withdrawn from the bank accounts of Thaksin's son, Panthongtae Shinawatra, over the period in question.

The authorities did not say who the money was transferred to. Transactions by others on the list were much smaller.

Critics said the government was harassing its opponents, many of whom have had their financial dealings restricted.

"This is nothing more than political persecution," said Karun Hosakul, a member of Parliament allied with the "red shirt" protesters and among those suspected of unusual transactions.

"The government is constantly sticking a knife into us every chance they have." Prime Minister Abhisit Vejjajiva has defended the move to restrict the transactions of suspects as necessary for national security, adding that legitimate requests to make financial transactions from these restricted accounts have been allowed.