Suu Kyi, Myanmar's toppled de facto leader and the National League for Democracy (NLD) party's head, had been kept in her house in Naypyitaw since the February 1 military coup.
"We don't know where she's being kept anymore," a senior NLD member told the news outlet.
Aside from Suu Kyi, the military arrested President Win Myint and other senior government officials, accusing them of electoral fraud and, later, breach of COVID-19 regulations on mass assembly limits. The military declared a one-year state of emergency and pledged to hold a new vote after then.
The coup triggered nationwide mass protests that remain ongoing. The majority of state institutions have by now renounced the military rule and joined the NLD-championed Civil Disobedience Movement.
In a separate development, the United Nations Special Envoy Christine Schraner Burgener told the UN General Assembly on Friday that the international community must not recognise or grant any legitimacy to the military rulers who seized power in Myanmar, toppling the democratically elected government there in a coup on 1 February.
"It is important that the international community does not lend recognition or legitimacy to this regime," Burgener, who was appointed by UN Secretary-General Antonio Guterres, told a special meeting of the General Assembly.
"There is no justification for the military's actions. There can be no business as usual under the current circumstances."