Min Min Soe, who is representing the deposed leaders, said she was not able to inform them about what was happening outside and is not allowed to meet her clients in person.
Their hearing was adjourned until April 12, Min Min Soe told reporters. Suu Kyi and Win Myint were arrested hours before the military's February 1 coup on several charges their allies say are fabricated.
Her chief lawyer, Khin Maung Zaw, told Reuters by telephone that Suu Kyi, three of her deposed cabinet ministers and a detained Australian economic adviser, Sean Turnell, were charged a week ago in a Yangon court under the official secrets law, adding he learned of the new charge two days ago.
A conviction under the law can carry a prison sentence of up to 14 years.
Hundreds of civilians have been killed in protests against the coup, according to the Assistance Association for Political Prisoners (AAPP) activist group.