- Mohamed Morsi died on Monday after collapsing in court.
- A judicial source said Morsi had fainted during a break in the trial hearing.
- The Brotherhood's political wing — the Freedom and Justice Party — accused Egyptian authorities of "deliberately killing him slowly".
- The military toppled him in 213 and kept him in detention.
Egypt's first democratically elected president Mohamed Morsi was buried on Tuesday in eastern Cairo, one of his lawyers told AFP, a day after he collapsed in court and died.
Rights groups called for an independent probe into the detention conditions and death of the Islamist, who was ousted in 2013 after a year of divisive rule.
State TV said the 67-year-old's death was due to a cardiac arrest.
"He was buried in Medinat Nasr, in eastern Cairo, with his family present," said Abdel Moneim Abdel Maksoud, one of his lawyer.
Morsi, also the country's first civilian president, had appeared "animated" during a hearing in a retrial over charges of collaborating with foreign powers and militant groups, judicial and security sources said.
"The court granted him his request to speak for five minutes... He fell to the ground in the cage... and was transported immediately to the hospital. A medical report found... no pulse or breathing," said the attorney general's office.
"He arrived at the hospital dead at 4:50 pm exactly and there were no new, visible injuries found on the body."
Another of Morsi's legal defence team described the moment he received news of his death.
"We heard the banging on the glass cage from the rest of the other inmates and them screaming loudly that Morsi had died," the lawyer, Osama El Helw, told AFP.
Since Morsi's overthrow on July 3, 2013, his former defence minister, now President Abdel Fattah al-Sisi, has waged an ongoing crackdown that has seen thousands of Muslim Brotherhood supporters jailed and hundreds facing death sentences.
A judicial source said Morsi had fainted during a break in the trial hearing.
The court officials "had just finished the session for the espionage case and they informed the judge that he had fainted and needed to be transported to a hospital where he later died," he told AFP.
Morsi last saw his family in September 2018. A month later, one of his sons, Abdallah, was arrested.
Abdel Maksoud was the last member of his defence team to see the former Islamist president, in November 2017.
The Brotherhood's political wing — the Freedom and Justice Party — accused Egyptian authorities of "deliberately killing him slowly".
They "put him in solitary confinement... they withheld medication and gave him disgusting food... they did not grant him the most basic human rights," it said in a statement.