Tajikistan has opened a criminal investigation after 14 prisoners were fatally poisoned while they were being transported between jails, the justice ministry said Monday, suggesting that another inmate may have given them contaminated bread.

The incident happened Sunday as more than 100 prisoners, including eight women, were being transferred in a convoy from prisons in the north of the Central Asian country to jails in the south.

The justice ministry said in a statement that a prisoner ­handed around bread to a group of 16 inmates traveling in one of the vehicles during a stop on the journey. 

It said that "16 prisoners, who were in the back of one of the cars, experienced nausea, dizziness, vomiting" half an hour after consuming the bread. 

Medical staff were only able to save the lives of two of the prisoners, according to the statement, which was relayed by the Khovar state information agency.

The state prosecutor had opened a criminal case into the incident, the ministry said. 

It comes after a riot inside a prison close to the country's capital Dushanbe in May left 32 people dead including three guards, sparking fears over the security of prisons in the country. 

Authorities blamed the Islamic State group for the riot.