Myanmar Commander-in-Chief Min Aung Hlaing has written to Prime Minister Prayut Chan-o-cha explaining why the Tatmadaw had to stage a coup to seize power and asked for help to support democracy.
Gen Prayut revealed about the letter on Wednesday.
Gen Prayut said the letter asked Thailand to support the democracy of Myanmar, which he said he always supports.
Yet he said he won't interfere in the neighbouring country's internal affairs as agreed under the Asean principle and the Treaty of Amity and Cooperation in Southeast Asia (TAC).
"At the very least, we are supportive of the democratic process in Myanmar, while what we also have to do is maintain relations [with Myanmar] as well as possible because that will benefit all Thai people and border trade [with the neighbouring country]," Gen Prayut said.
"Thailand supports the democratic process. The rest is up to him to see how to proceed."
On Tuesday, Gen Prayut said he didn't want anti-Myanmar coup protests to take place in Thailand and warned certain groups against provoking unrest linked to the coup.
He said it was a "sensitive issue and needs to be dealt with with prudence".
As for calls by Malaysian and Indonesian leaders for Asean to convene a special meeting to discuss Myanmar's internal issues, Gen Prayut said he would leave it up to Asean.
Since the coup last week, Myanmar has been convulsed by the biggest protests in more than a decade as Aung San Suu Kyi's supporters challenge the coup that halted a tentative decade-long transition to democracy.
Protesters took to the streets of Myanmar for a fifth day on Wednesday, vowing to keep up demonstrations against the coup even after a woman was shot and critically wounded during clashes the previous day.
The United States and United Nations condemned Tuesday's use of force against the protesters who are demanding the reversal of the Feb 1 coup and the release of deposed leader Ms Suu Kyi, and other leaders of her National League for Democracy (NLD).
"We cannot stay quiet," youth leader Esther Ze Naw said.
"If there is bloodshed during our peaceful protests, then there will be more if we let them take over the country."
Thousands of people joined demonstrations in the main city of Yangon. In the capital, Nay Pyi Taw, hundreds of government workers marched in support of a growing civil disobedience campaign.
A group of police in Kayah state in the east joined the protesters and marched in uniform with a sign that said "We don't want dictatorship".
There were no reports of violence on Wednesday, but soldiers took over a clinic that had been treating wounded protesters in Nay Pyi Taw on Tuesday, a doctor there said.
Another doctor said the female protester shot in the head during Tuesday's confrontation with police in Nay Pyi Taw was not expected to survive.
She was wounded when police fired, mostly into the air, to clear the protesters.
Three other people were being treated for wounds from suspected rubber bullets, doctors said.
Protesters were also hurt in Mandalay and other cities, where security forces used water cannon and arrested dozens.
Four policemen were injured on Tuesday as they tried to disperse protesters, some of whom threw stones and bricks, the military said.
The military has imposed restrictions on gatherings and a night curfew in the biggest cities.
The protests are the largest in Myanmar in more than a decade, reviving memories of almost half a century of direct army rule and spasms of bloody uprisings until the military began relinquishing some power in 2011.
The military has tried to justify its takeover by alleging fraud took place in a Nov 8 election that Ms Suu Kyi's NLD party won by a landslide, as expected.
The country's electoral commission dismissed the army's complaints.
Western countries have condemned the coup but taken little substantive action to press for the restoration of democracy.
The US State Department said it was reviewing assistance to Myanmar to ensure those responsible for the coup faced "significant consequences".