Sheikh Mujib became the country's first president
The Bangladesh proclamations of independence - drafted on paper during the war against Pakistan in 1971 - have gone missing, officials say.
They say that it is unclear when the historic documents disappeared.
Officials say it was only discovered they were missing when the government handed over important artefacts to the national archive in April.
The documents were drafted on behalf of imprisoned Bangladeshi independence leader Sheikh Mujibur Rahman in 1971.
Sheikh Mujib was jailed at the time in what was then West Pakistan, but was released from captivity to become the first president of independent Bangladesh in January 1972.
Cabinet Secretary Ali Imam Majumder told The Daily Star newspaper that officials in the cabinet division could not find the original versions of the hand-written independence proclamations.
Events leading up to independence were violent and turbulent
"We only had photocopies, which we handed over to the national archives," he said.
He told the newspaper that he did not know how the originals had gone missing.
Bangladesh's first Cabinet Secretary, HT Iman, told the Daily Star that the original proclamation of independence had definitely been placed in government custody.
He said that it was "really unfortunate" for the nation that it and other promulgations had now disappeared.
Experts who drafted the proclamation of independence say that it worked as a provisional constitution of Bangladesh throughout the war.
Historians say that the constitution had to be handwritten because for most of 1971 Bangladesh was in turmoil as thousands of people died in the struggle for independence.
Some former government officials say that the independence promulgations could have been lost, removed or destroyed by the military government which seized power in the country in 1975.
However officials say that photocopies of some of the promulgations - signed by all the country's cabinet ministers except the incarcerated Sheikh Mujib - do still exist.
The promulgations served as an interim constitution for the country until a new constitution was drafted in December 1972.