According to the BBC Sirikit had "suffered several illnesses" while in hospital since 2019, including a blood infection this month, it added.
For more than six decades, Queen Sirikit was married to Thailand's longest-reigning monarch King Bhumibol Adulyadej, who died in 2016.
King Vajiralongkorn has ordered the Thai Royal Household Bureau to organise a royal funeral, the statement added.
Queen Sirikit's body will lie in state at the Grand Palace's Dusit Thorne Hall in Bangkok, according to the palace.
Thai royal family members will also observe a year of mourning.
