Burma's Prime Minister Soe Win is being treated at a hospital in Singapore, an official from the Burmese embassy in the city-state said.
Soe Win was made prime minister in 2004
The official would not give details of Soe Win's illness, saying only that it was a "serious health matter".
The Irrawaddy, a publication run by Burmese journalists in exile, reported last week that the prime minister may be suffering from leukaemia.
Soe Win, in his late 50s, has been prime minister since 2004.
An army general, he replaced the ousted former prime minister Khin Nyunt.
Soe Win is reported to be receiving treatment in the same hospital attended by Burma's 73-year-old military leader Than Shwe, in January.
The embassy official said Soe Win had arrived in Singapore at the end of last month, and did not know when he would be discharged from hospital. He gave few other details.
"From our embassy's side, we give a lot of logistical support, but for the medical side, it's being taken care of by the hospital, so we are not in the position to comment," the official was quoted by the Associated Press as saying.