The State Department said Sunday it was "deeply concerned" for the health of Suu Kyi, saying she has started a hunger strike. The agency did not explain how it got that information.
Germany and Britain also expressed concern Monday and urged that the Nobel Peace prize laureate be immediately released.
"The (U.S.) statement is groundless," Myanmar's Foreign Ministry said in a statement. It urged the United States to state the source of the claim so it could verify the allegation.
Suu Kyi was arrested May 30 following a bloody confrontation between her followers and the regime's supporters in northern Myanmar. The government has claimed she was detained for her own protection and for the sake of national stability.
Her detention and the arrest of senior members of her National League for Democracy party triggered international outrage, with the United States imposing tougher economic sanctions.
The government refuses to say where she is being held or how long she will stay in detention.
British Foreign Office Minister Mike O'Brien spoke Monday with Myanmar's ambassador, Kyaw Win, and told him Britain holds Myanmar responsible for Suu Kyi's welfare.
"It is now exactly three months since Aung San Suu Kyi was detained under measures that were described by the regime as temporary, after she and her supporters were attacked in a deliberate and premeditated way," O'Brien said.
Germany's human rights representative, Claudia Roth, said Monday that she expects Myanmar's government to "deliver without delay" on its July promise it would soon release Suu Kyi.
Alfredo Mallet of the International Committee of the Red Cross said he cannot confirm the hunger strike report since his office has not met with Suu Kyi since July 28.
On Saturday, the newly appointed prime minister, Gen. Khin Nyunt, announced a "road map" to national elections and a new government, but made no offers to hold talks with Suu Kyi. He also gave no timetable for the promised "free and fair" elections.
The current junta came to power in 1988 after crushing a pro-democracy uprising in Myanmar. It called elections in 1990 but refused to hand over power when Suu Kyi's NLD party won.
Since 1990, Suu Kyi has been kept under various periods of house arrest. Her latest detention halted reconciliation talks she had begun with the junta in October 2000.
She won the Nobel Peace prize in 1991.
Written By AYE AYE WIN