Three prisoners who were transferred to solitary confinement after they were tested positive to illicit substances have been on a hunger strike since Wednesday, the government said.
It said in a statement the prisoners were also stopped from continuing with their work at the prisons as was the norm in such circumstances.
It said the prisoners concerned were in a good state of health was the prison's medical staff was keeping an eye on them.
Shadow minister Beppe Fenech Adami said the statement showed that the government had failed in its promise to eradicate drugs from prison.