Egypt's former spy chief Omar Suleiman died early on Thursday aged 76 whilst undergoing medical tests in the United States.
"He was fine, it happened all of a sudden," Hussein Kamal, the head of Suleiman's presidential campaign team and head of his personal office, told Reuters. "He was undergoing medical examinations," he added, without revealing the cause of death.
Meanwhile, Sky News Arabia quoted an anonymous source stating that Suleiman had been suffering from a blood disease, which led to his death in a Cleveland hospital at dawn Thursday.
Egypt's state-run news agency MENA claimed Suleiman had developed a lung disease months ago, which later caused heart problems. His health notably deteriorated over the past three weeks, it added.
An Egyptian diplomatic source in Washington told MENA that arrangements were being made to transfer his body back to Egypt. The same source said two of Suleiman's daughters were escorting him.
Suleiman was a husband and father of three daughters.
His military funeral will take place Friday in Cairo and will be attended by Field Marshall Tantawi, the head of the quasi-ruling Supreme Council of the Armed Forces, according to an unnamed intelligence source.
As spy chief Suleiman was not in the public eye but he hit the headlines after being appointed vice-president by ousted president Hosni Mubarak during last year's uprising.
Under pressure from mass protests in Cairo's Tahrir Square and around the country, a compromise deal was floated, whereby Suleiman would assume the president's powers for the remainder of Mubarak's term, along with a pledge by the then-president that he would not to run again for the post.
Suleiman's tenure as vice-president lasted for just a few days as Mubarak was deposed shortly after his appointment.
It was Suleiman who, in a short TV address on 11 February 2011, announced that Mubarak had stepped down and handed over his powers to the Supreme Council of the Armed Forces (SCAF).
For a while afterwards, Suleiman all but vanished from the political scene, but returned after announcing his intention to run for president.
However, his presidential bid was blocked by the Supreme Presidential Electoral Committee (SPEC) because he failed to acquire the number of recommendations stipulated by the election law.
During Suleiman's short-lived presidential bid he portrayed himself as a staunch enemy of the Muslim Brotherhood and Islamist forces.
In the final years of Mubarak's reign, he was one of the key architects of the blockade of the Gaza Strip.
Suleiman reportedly warned that Egypt would suffer unpleasant ramifications if Mohamed Morsi, a senior figure in the Brotherhood, was elected president.
Morsi was inaugurated as Egypt's president late last month.