The son of Egypt's one and only democratic President Mohammed Morsi thanked President Recep Tayyip Erdoğan for his support following his father's death last week.

"We would like to thank everyone, particularly Mr. Erdoğan, Qatari Emir Tamim bin Hamad al-Thani and his father [Sheikh Khalifa bin Hamad Al Thani], the Malaysian government and former Tunisian President Moncef Marzouki," Morsi's son, Abdullah, told Al-Jazeera on Sunday.

Abdullah said Egyptian authorities did not allow his family to organize a condolence ceremony for his father and that a funeral prayer in absentia was held in Al-Aqsa mosque in Jerusalem.

Millions of people around the world attended the funeral prayers for his father, he said. "No such event has ever been witnessed in history. Never have millions of people performed funeral prayers in absentia for anyone," he said.

Morsi, 67, died Monday after falling unconscious inside his soundproof glass cage during his trial on "espionage" charges, which he along with numerous human rights groups and independent observers said were politically motivated.

Activists and his family have long maintained that he was not receiving treatment for a host of health problems including diabetes.

In an Istanbul address on Wednesday, Erdoğan said Morsi did not die a natural death, but was murdered.

He vowed to pursue justice for Morsi's sudden and unexplained death.

"Turkey will do whatever it takes to prosecute Egypt [regime] in international courts," he said, urging the Organisation of Islamic Cooperation (OIC) to take action.

"We will also raise the issue at the G20 meeting in Osaka," he added.

Besides Turkey and Palestine, absentee funeral prayers were held in Ethiopia, Somalia, Syria and the Xinjiang Uighur autonomous region in China, among others places.

Morsi was elected president in 2012 but was ousted in a military coup a year later. The military crushed the Muslim Brotherhood movement in a major crackdown, arresting Morsi and many others of the group's leaders, who have been in prison undergoing multiple trials ever since the coup.

He reportedly died from a heart attack last Monday during a court session. The country's state television reported early Tuesday that Morsi was "suffering from a benign tumor, had continuous medical attention and his death was caused by a heart attack." Amnesty International and other rights groups have called for a fair, transparent and comprehensive investigation into Morsi's death and raised questions about his treatment in prison. Egypt's government has dismissed accusations that he was badly treated.