(CNN) Abdullah Morsy, the son of ousted Egyptian President Mohamed Morsy , has accused the country's current regime of "slow ... murdering" his father, amid wider questions from human rights groups about how the late leader was treated in prison.

The 67-year-old, who collapsed and died in a Cairo court on Monday , had been detained since he was ousted in a military coup in 2013 after he became Egypt's first democratically elected leader a year earlier.

"Seven years of siege and total isolation ... he has complained more than once to the court that his life is in danger and that he needs medical care, but he was denied it," Abdullah Morsy told CNN.

"Of course there is a criminal suspicion against this repressive regime and its security apparatus. All these actions represent a slow deliberate medical murdering."

CNN requested comment from the Egyptian government and has not yet received a response.

Abdullah Morsy says his father was buried in the Nasr City district of eastern Cairo early on Tuesday alongside other senior figures of the Islamist Muslim Brotherhood Muslim Brotherhood movement.

An Egyptian police vehicle is parked inside a cemetery in Nasr City after the former Egyptian President Mohamed Morsy was buried.

He added that he washed the ex-president's body in Cairo's Tora prison hospital early Tuesday with Morsy's three other sons and his father's lawyer Abdel Moneim Abdel Maqsoud. They then read prayers for him in the prison mosque, finishing at 5 a.m.

Authorities had refused Morsy's request in his will to be buried at his family cemetery in his home province of Sharqiya, according to his son. However, Abdullah Morsy added that the family did not mind, because the Muslim Brotherhood cemetery was "a good place."

"They were his friends and companions of a long journey struggle," he added.

Morsy fell unconscious on Monday after making a final statement in his trial on espionage charges, Egypt's public prosecution office said in a statement.

Morsy's lawyer Abdel Maqsoud told CNN that the former president spoke for seven minutes before the session was adjourned. Morsy was then led back to a soundproof glass cage in the courtroom.

"A minute after, we saw fuss in the court glass box, we could hear the defendants screaming, Dr. Morsi has fallen," said Abdel Maqsoud, who is also the lead lawyer for the banned Muslim Brotherhood.

Morsy had closed his final statement by quoting a verse of a poem that read, "My country is dear even if it oppressed me and my people are honorable even if they were unjust to me," Abdel Maqsoud said.

According to Egypt's state-run Al Ahram, Morsy suffered a heart attack. The prosecutor's office said he was pronounced dead after arriving at hospital at 4:50 p.m. (10:50 a.m. ET) and that no apparent injuries were found on his body.

According to Islamic law and Egyptian tradition, the deceased should be buried as soon as possible. Muslim burial rites are commonly performed the same day or within 24 hours of death.

International calls for authorities to be investigated

Human Rights Watch (HRW) called for Egyptian authorities to be investigated for the "mistreatment" of Morsy, saying he suffered years of insufficient access to medical care while he was in prison.

Leading up to his death, HRW's Middle East and North Africa director Sarah Leah Whitson said Morsy faced mistreatment, prolonged solitary confinement, inadequate medical care and was deprived of family visits and access to lawyers.

Here's what we said TWO years ago about #Egypt Pres #Morsy cruel and inhumane imprisonment (on trumped up BS charges), solitary confinement, deprived of family visits and medical care. Nothing improved. Predictable outcome of govt's criminal negligence. https://t.co/TEm2mEEBPK — Sarah Leah Whitson (@sarahleah1) June 17, 2019

"At the very least, the Egyptian government committed grave abuses against Morsy by denying him prisoners' rights that met minimum standards," Whitson said.

HRW previously reported that Morsy was diabetic and that he had fainted several times and experienced a diabetic coma.

Human rights groups also cautioned that his poor health (in addition to diabetes, he also had liver and kidney ailments) would lead to his premature death.

Abdullah told CNN that the family was denied permission to visit him and that they had been allowed to see him "only three times since 2013."

In response to HRW's report regarding Morsy's health, the Egyptian government called it "nothing but political exploitation in the name of human rights" and said it was a "new ethical low for Human Rights Watch."

Morsy pictured in 2014 inside a defendant's cage.

The statement from Egyptian State Information Service said Whitson's tweets about the circumstances of Morsy's death contained "false claims," adding that Morsy had submitted his last official request regarding his health to the court on November 19, 2017, "asking to be treated on his own expense, and the court approved his request."

Following his death, Amnesty International also said in a tweet that an investigation was an "urgent requirement," which included a look into the conditions of his detention. It cited Egypt's "proven track record of holding prisoners in solitary confinement for long periods and in harsh conditions."

In a statement on Monday, the Muslim Brotherhood said it held current President Abdel Fattah el-Sisi and his regime "accountable for the killing of the elected legitimate president, politically and criminally," and demanded an independent review into the circumstances of Morsy's death.

At a funeral in absentia organized for Morsy at Fatih Mosque in Istanbul, Turkish president Recep Tayyip Erdogan said he didn't believe Morsy died a normal death, and that authorities are "so scared that they cannot give Mohamed Morsy to his family."

"Mohamed Morsy has a testament that he says he wants to be buried in his village. These people did not accept this. Sisi continues his cruelty here as well. Brothers don't forget that those who are scared cannot make a statue of victory," he added as a crowd chanted: "Murderer Sisi will be held to account!"

A polarizing figure

Educated in southern California and a strict Islamist, Morsy was voted into power in June 2012 following the 2011 Arab Spring uprising that toppled Hosni Mubarak's longstanding rule.

Morsy -- a senior member of the Muslim Brotherhood — campaigned on appealing to the broadest possible audience, however during his year in power critics say he became an authoritarian leader who forced through a conservative agenda.

Both he and the political wing of the Muslim Brotherhood movement were ousted in a coup in 2013, with the Muslim Brotherhood declared a terrorist organization and banned by the government after the military seized power.

The Muslim Brotherhood is a religious and political group founded on the belief that Islam is not simply a religion, but a way of life. It advocates moving away from secularism and returning to the rules of the Quran as a basis for healthy families, communities and states.

In August 2013, roughly 1,000 Egyptians -- many of them Morsy supporters -- were killed during protests against the military government.

Morsy addresses suporters at a press conference on June 13, 2012.

He was sentenced to death in 2015 over a jailbreak during the 2011 uprising and to life in prison on espionage charges after being convicted of conspiring with Palestinian group Hamas, the Iranian Revolutionary Guard and other foreign organizations.