The top aide of caretaker Prime Minister Thaksin Shinawatra yesterday passed responsibility to the foreign ministry to deal with growing calls on the government to reveal the content of a controversial letter the premier sent to US President George W Bush.

Prommin Lertsuridej, the prime minister's secretary-general, said the ministry would decide whether the contents of the letter could be released.

Kiattikhun Chartprasert, a deputy spokesman at the ministry, said it was not in line with diplomatic protocol to reveal the content of letters between the heads of government.

He indicated it would be up the person who wrote the letter to decide whether it should be released.

The ministry will continue to look into the matter after the long weekend, he said.

Prommin reiterated yesterday that the letter was not personal and that it had been sent through proper diplomatic channels.

News of the letter sparked

controversy after outgoing Sena-tor Kraisak Choonhavan said Thaksin had written to Bush to allegedly complain about attempts to topple him by undemocratic means.

Kraisak claimed the letter contained allegations that were similar to those made by Thaksin to top bureaucrats on June 29 when he claimed a person with "undemocratic" power was trying to overthrow him.

Thaksin's opponents have decried the ambiguous allegation, and Kraisak's disclosure has fanned controversy, with the caretaker leader now being accused of trying to defame his rivals on the global stage as well as behaving as though Thailand was "a US colony".

Prommin said on Saturday the letter might be released to the

public after the long weekend, but yesterday he said it was up to the foreign ministry to decide.

"This is because the letter deals with bilateral relations. [The

ministry] will take diplomatic protocol into account when deciding if all or part of the letter can be disclosed," he said.

He said the letter had been sent to Bush to prevent bilateral relations from being disrupted.

Thai Rak Thai Party spokesman Sita Divari said Thaksin's letter was nothing more than normal communication between the two national leaders. He said Thaksin had communicated with other country leaders several times since the Thai Rak Thai became the ruling party.

Sita said Kraisak might be unaware of the real content of the letter.

The spokesman said the party lawyers would consider whether the party should file a defamation suit against Kraisak for damaging its reputation.