YANGOON: Myanmar opposition leader Aung San Suu Kyi is "not in good health" as she cannot eat, while her doctor is being detained by police, her party spokesman told AFP on Saturday.

The 63-year-old Nobel Laureate, whose detention comes up for renewal in late May, has low blood pressure, is dehydrated and has been placed on an intravenous drip by her doctor's assistant, Nyan Win said.

"The lady's not in good health. She cannot eat and she has low blood pressure," Nyan Win said. He added that she "has dehydration".

"We are worried very much for the lady's health situation," the National League for Democracy spokesman said.

In her doctor's absence, medical assistant Pyone Moe Ei had spent three hours on Friday afternoon at Aung San Suu Kyi's lakeside prison home and has requested permission to return today to renew the intravenous drip, he said.

Nyan Win said he did not know why the doctor had been held by police since Thursday.

Official sources said on Thursday the physician, Tin Myo Win, had been denied permission to enter the house after waiting several hours to carry out a regular medical check-up on the pro-democracy leader.

A day earlier Myanmar authorities arrested a US national after he swam across a lake to the off-limits compound where Aung San Suu Kyi has been isolated under house arrest for most of the past 19 years.

State media said the man, identified as John William Yeattaw, spent two days at the house before security forces plucked him from the water as he left at dawn.

Official sources said today the 53-year-old man had slept for two days on the ground floor of Aung San Suu Kyi's house, where her two maids live, and asked the detained leader not to inform authorities he was there.

The man's motive remained unclear but official sources have said he is a Vietnam war veteran, while Aung San Suu Kyi's lawyer Kyi Win told AFP Yeattaw was an "adventurous" American acting of his own accord.

Aung San Suu Kyi lives with her two maids and is allowed only occasional visits from her doctor and lawyer.

A roadblock stopping cars driving near her home was removed today while heavy security that was put in place following the breach was relaxed.

The opposition leader's latest period of incarceration expires at the end of May and authorities have not said if they intend to extend her sentence, though Western diplomats say she is not likely to be released.