President Bush has criticised Myanmar's military government over its treatment of pro-democracy protesters demonstrating against rising fuel prices.
In a statement the US president said he "strongly condemns the regime for arresting, harassing and assaulting" the activists, and called for those who have been jailed to be released.
At least 100 people have been arrested over a series of demonstrations against a rise in petrol prices.
In his statement Bush said the activists were merely voicing concerns about recent price hikes "and their concerns should be listened to by the regime rather than silenced through force."
The government should also "stop its intimidation of those Burmese citizens who are promoting democracy and human rights" and "release all political prisoners, including Aung San Suu Kyi, and ... lift restrictions on humanitarian organizations that seek to help the people of Burma," he said.
Myanmar was formerly known as Burma until the military government changed the country's name in the 1990s.
Hunger strike
Prominent activisit Su Su Nway says she has gone into hiding fearing arrest [AFP]Bush's condemnation of Myanmar's military followed news that a group of pro-democracy protesters arrested after protests in Yangon last week had launched a hunger strike.
They are reportedly demanding medical treatment for a colleague who broke his leg when police and pro-government militia broke up a protest in Yangon and arrested up to 20 people on Tuesday.
"Some of the people arrested with him started a hunger strike this evening because their colleague Ye Thein Naing hasn't received any medical treatment for his broken leg," one activist told AFP news agency on condition on anonymity on Thursday.
Ye Thein Naing and an unknown number of other protesters are being held at an improvised detention centre at the city's Kyaikkasan sports grounds, he said.
Hiding
Like many of the protesters, Ye Thein Naing is a member of the opposition National League for Democracy (NLD), headed by Aung San Suu Kyi, the Nobel peace prize winner who is currently under house arrest.
Su Su Nway, another NLD member and labour activist who led the march on Tuesday, said that she and other leaders of the protest movement have gone into hiding to avoid arrest.
"I heard the authorities have been watching my house all the time, waiting to arrest me," she said.
"We have only pens and books. I do not understand why they treat us like rebels.
"We are just making a statement on behalf of the people, including government staffers. We are sacrificing our young lives. I want the authorities to understand that."
The NLD won a landslide victory in general elections in 1990 elections, but the military has never recognised the result.