Ousted Myanmar democracy figurehead Aung San Suu Kyi is in "strong spirits", her son told AFP Tuesday after receiving a letter from her -- their first communication since she was detained in a coup three years ago.

"She is in strong spirits as always," Kim Aris said of the letter he received from his mother, who is being held in the military-built capital Naypyidaw.

Suu Kyi was detained on the morning of the coup in February 2021 and has since been sentenced to prison for more than 20 years, after what rights groups say was a sham trial in a junta court.

She has been largely hidden from view since, appearing only in grainy state media photos at her trial.

The letter received in early January was "the first real indication I've had... that she's actually alive", Aris told AFP by phone from London.

Myanmar has been in turmoil since the coup. A military crackdown on dissent has killed more than 4,400 people and seen more than 25,000 arrested, according to a local monitoring group.