A major human rights organization in Britain has documented numerous cases of prisoner deaths in Egypt, saying the government is turning a blind eye to "the slow-motion executions" of those behind bars for expressing their beliefs.

The “Graves of the Living,” a Monday report issued by the London-based Arab Organization for Human Rights (AOHR), recorded at least 40 deaths of prisoners in Egypt only in the month of August, 2015.

AOHR said 20 of the victims died from “medical negligence” while five more were subject to “torture” by Egyptian prison authorities. It added that 13 prisoners were victims of suffocation, overcrowding and blistering heat, and one died from poisoning. The fate of one prisoner remains undetermined, the report said.

The NGO said that 19 of the prisoners were in preventive custody, and had yet to face any formal charges.

Egypt has seen a rise in the number of prisoner deaths over the past months with most of the cases related to political activists and members of the Muslim Brotherhood, the biggest political party in the country which has been officially banned by the government.

Many say the government is to blame for the growing trend, as it abandons those in need of medical care to die in prison facilities. Egypt’s former president and the most prominent political prisoner, Mohammed Morsi, who was toppled and arrested in July 2013, once claimed that prison authorities wanted to kill him through poisoned food.

The AOHR called on the United Nations to send a fact-finding mission to Egypt to inspect the situation in detention facilities, and prevent what it called the “slow-motion executions” of people.

It said the main reason behind such escalated trend of human rights violations is the “impunity” the government has given to security officials.

The Arab African Center for Freedoms and Human Rights, which is based in Cairo, published a report earlier this month, documenting 42 deaths of dissidents whilst in police custody in August.

The former army chief and current President Abdel Fattah el-Sisi has been engaged in a massive crackdown on protesters over the past two years, killing hundreds of political activists, mostly affiliated to the Muslim Brotherhood. Many others have died inside detention facilities while the judiciary has sentenced hundreds more to death.