The court's decision marks the first time a former leader of the armed forces has been convicted of treason and sentenced to death in Pakistan, where the military maintains strong influence and senior officers are often considered immune from prosecution.

Musharraf has been in self-imposed exile ever since a travel ban was lifted in 2016 that allowed him to seek medical treatment abroad.

The 76-year-old has lately spent most of his time between Dubai and London.

Several Pakistan media sources reported the verdict and sentence handed down by a three-member special court, while a senior judicial official confirmed the rulings to AFP.

Pakistan's military siftly slammed the special court's ruling, saying in a statement that the armed forces were in "pain and anguish" over the decision.

"An ex-Army Chief, Chairman Joint Chief of Staff Committee and President of Pakistan, who has served the country for over 40 years, fought wars for the defense of the country can surely never be a traitor," the military said in a statement, adding the legal process "seems to have been ignored".

The trial -- which began in 2013 and is one of several involving Musharraf -- centred on his decision to suspend the constitution and impose emergency rule in 2007, according to his lawyer Akhtar Shah.

The move sparked widespread protests against Musharraf, ultimately leading to his resignation in the face of impeachment proceedings.

Musharraf's lawyer said the former general was currently ill and remained in Dubai. He said no decision had been made on whether to appeal.

The court ruling comes more than a week after Musharraf slammed the ongoing treason case against him in a video message showing the former general in a hospital bed appearing ill, while complaining of dizziness and blackouts.

"I think this case is baseless, they are not listening to me and they are not listening to my lawyer... it is a big injustice," said Musharraf.

Retired general Talat Masood, now a security analyst, called the court's decision "extraordinary" and "bold".

- 'Revenge' -

Musharraf, who was born in India's capital Delhi in 1943 but moved with his family to Pakistan after partition, took power after ousting Prime Minister Nawaz Sharif in a bloodless coup in 1999.

A cigar-smoking, whisky-drinking moderate, the general became a key US ally in the "war on terror" after the September 11 attacks and escaped at least three Al-Qaeda assassination attempts during his nine years in office.

His rule faced no serious challenges until he tried to sack the chief justice in March 2007, sparking nationwide protests and months of turmoil that led to the imposition of a state of emergency.

After the December 2007 assassination of former prime minister Benazir Bhutto, the national mood soured even further and he was left isolated by the crushing losses suffered by his allies in February 2008 elections.

Musharraf finally resigned in August 2008 in the face of impeachment proceedings by the new governing coalition and went into exile.

He returned in 2013 in an attempt to contest elections, but was barred from taking part in the polls and from leaving the country as a barrage of legal cases mounted.

The treason case was first launched against Musharraf by his old foe Sharif in 2013. The case went on for years amid repeated delays until Tuesday's surprise announcement.

The treason ruling is the latest case to target Musharraf since he has been in exile.

In 2017, a Pakistani court pronounced him a fugitive in the murder trial of Bhutto -- the first woman prime minister of a Muslim country.

The anti-terrorism court also branded Musharraf an absconder and ordered the confiscation of his property.

Musharraf is alleged to have been part of a broad conspiracy to have his rival Bhutto killed before elections. He has denied all charges.

Following the court's decision Tuesday, Bhutto's son Bilawal Bhutto Zardari tweeted: "Democracy is the best revenge".