The former prime minister was sentenced to three years for violating the official secrets act, on top of a 20-year sentence already handed down by the military junta that took power in 2021.
The ousted leader, who has been detained since last February's military takeover, is already being tried on five other corruption charges. Each is punishable by up to 15 years in prison and a fine.
Suu Kyi was convicted last month on two other charges and given a four-year prison sentence, which was then halved by the head of the military-installed government.
The move comes days after a regional bloc of nations snubbed the country's ruling junta, disinviting coup leader Min Aung Hlaing from an upcoming summit.
Myanmar's ousted leader, once an icon of freedom, faces the prospect of another prolonged detention. But her handling of atrocities against the Rohingya has left her reputation abroad in tatters.
The remarks by Myanmar special envoy Christine Schraner Burgener during a closed-door session of the U.N. Security Council come as new fighting rages between the army and ethnic insurgents.
Many of those who led the first protests against Myanmar's coup were minority rights activists, garment workers, student groups and others who had butted heads with Aung San Suu Kyi and her party.
Myanmar imposed martial law in parts of the country's largest city after a crackdown on peaceful protests opposing last month's military coup resulted in the deaths of at least 38 on Sunday.
The detained former leader appeared for a hearing Monday, a month after being ousted in a coup, as her supporters staged protests, despite a deadly crackdown by police.
The Treasury Department froze the assets of 10 current and retired top-ranking military leaders in Myanmar after a coup earlier this month that toppled the government of Aung San Suu Kyi.
A week after Myanmar's military seized power, it imposed restrictions in major cities to quell growing protests, as the coup's leader promised a new election in his first televised address.
Calling for the release of detained de factor leader Aung San Suu Kyi and chanting anti-military slogans, protesters amassed across the country Sunday demanding an end to the military takeover.
Days after a coup and the detention of Aung San Suu Kyi and other elected leaders, the country's military is moving to strangle free speech by shutting down access to social media sites.
