Pakistan's former military ruler Pervez Musharraf failed to show up for a hearing in the treason case against him on Wednesday, with his lawyers citing security threats.

The 70-year-old stands accused over his imposition of emergency rule in November 2007, but he and his legal team have dismissed the charge as politically motivated.

Conviction could mean the death penalty or life imprisonment for Musharraf, who has faced a series of criminal cases since returning from self-imposed exile in March.

His defense team said he could not attend the treason tribunal on Wednesday because security arrangements were inadequate. They also complained that lawyers in the case had been threatened.

Officials said police defused a bomb near the house of the former president hours before he was to appear in court.

Police officer Nayyar Saleem says officials scanning the route to court spotted the improvised bomb along a road about two kilometers from Musharraf's farmhouse.

"He is unable to appear before the court because of security hazards," lawyer Ahmed Raza Kasuri said.

The Taliban have made repeated threats to kill Musharraf, who led Pakistan into its alliance with Washington's "war on terror", and he lives under heavy guard at his farmhouse at the edge of Islamabad.

The case was adjourned on Dec 24 after explosives were found along the route he was to take to court and on Monday more explosives were discovered on the same road.

Musharraf is the first former army chief to go on trial in Pakistan, setting up a potentially destabilizing clash between the government -which brought the charges - and the all-powerful military.

On Sunday, the retired general denounced the treason case as a "vendetta" against him and claimed he had the backing of the military.

"I would say the whole army is upset. I have led the army from the front," he told reporters at his home.

"I have no doubt with the feedback that I received that the whole army is ... totally with me on this issue."

There has been no public comment on the case from the army, but some observers say they are reluctant to have their former chief suffer the indignity of trial in a civilian court.

The potential for the case to disrupt Pakistan's delicate civilian-military balance means it will be keenly watched by the US and NATO as they wind down their mission in Afghanistan.

Pakistan's cooperation and access through its territory is crucial as NATO pulls out military equipment built up over more than a decade of war.

The allegations are the latest in a series of criminal cases faced by Musharraf since he returned to Pakistan in a thwarted bid to run in May's general election.

These include murder charges over the assassination in late 2007 of former prime minister Benazir Bhutto.

The former commando's lawyers have dismissed the charges as an attempt by the government of Prime Minister Nawaz Sharif, whom Musharraf ousted in a coup in 1999, to settle old scores through the courts.

Musharraf spokesman Raza Bokhari said they have filed challenges to the tribunal's authority.

"We demand that the unlawfully formed special treason court avoid the label of being called a 'kangaroo court' and suspend its proceedings until the challenges raised by General Musharraf are heard and properly disposed by the superior courts," Bokhari said in a statement issued late on Tuesday.

They have urged the United Nations to intervene in what they call a "stage-managed show trial" and have asked London and Washington to "repay their debt" for Musharraf's support in the wake of the 9/11 attacks.

AFP-AP