Myanmar's opposition party has said Aung San Suu Kyi, its leader, is in poor health - she is not eating, is dehydrated and has low blood pressure.

Nyan Win, the spokesman for Suu Kyi's National League for Democracy (NLD), said on Saturday that the opposition leader, who has spent most of the past 19 years under house arrest, is "not in good health".

Nyan Win said the assistant to Suu Kyi's doctor had been to visit her on Friday and placed her on an intravenous drip.

"The lady's not in good health. She cannot eat and she has low blood pressure and she [the assistant] found she [Suu Kyi] has dehydration," he said.

Doctor arrested

"We are worried very much for the lady's health situation."

Pyone Moe Ei, the medical assistant, had spent three hours on Friday afternoon at Suu Kyi's house and has requested permission for a return visit on Saturday to renew the intravenous drip, he said.

Authorities arrested Tin Myo Win, Suu Kyi's doctor, on Thursday after he went to the house to carry out a regular medical check-up on the opposition leader.

Official sources said the he had been denied permission to enter the house, but it was not explicitly stated why he had been detained.

Secret visit

On Wednesday, Myanmar authorities arrested a man identified as John Willian Yeattaw, a US national, after he swam across a lake to the off-limits compound where Suu Kyi is under house arrest.

State media said the man confessed to secretly entering the house.

It is thought to be the first time anyone has successfully sneaked into Suu Kyi's compound, or swam across the lake in an attempt to get there

The man reportedly spent two days there before security forces arrested him when he tried to swim away.

Under house arrest, Suu Kyi is allowed only occasional visits from her doctor and lawyer.

The NLD won a landslide victory in elections in 1990 but the  military, which has ruled Myanmar since 1962, has never allowed the party to take office.