Pakistan's former military leader Pervez Musharraf was formally charged by a court on Tuesday with murdering Benazir Bhutto, the ex-prime minister who was assassinated at a political campaign rally in 2007.

Musharraf was indicted during a short hearing at a court in the city of Rawalpindi, a move that adds to the problems facing the former president who returned from self-exile in March only to be entangled in three legal cases, barred from contesting elections and put under house arrest.

Public prosecutor Mohammad Azhar told reporters that the 70-year-old retired general was charged with murder, conspiracy to murder and facilitation of murder during a short hearing.

Musharraf's lawyer said he denied all the all the charges and the cases against him were fabricated.

Militant groups have vowed to kill the former army chief, who was whisked to court under heavy security, with hundreds of police positioned along the road to the court.

Bhutto warned before her death that Musharraf should be held responsible if she was assassinated. His government was widely criticised for not doing enough to protect Bhutto when she returned to the country in 2007.

Nonetheless, many respected lawyers say the case against him is flimsy.

They believe the prosecution will struggle to prove a link between Musharraf and the assassination of Bhutto, who died after a gun and bomb attack on her car as she left a campaign rally in Rawalpindi.

At the time, Musharraf's government blamed the assassination on Baitullah Mehsued, the Pakistani Taliban chief who was killed by a US drone strike in 2009.

Heraldo Muñoz, an assistant secretary general of the UN and chairman of a panel that investigated the death of Bhutto, has said there is no "proof of culpability" against Musharraf.

But Musharraf does bear "political and moral responsibility for the assassination", Muñoz wrote in an extract of soon-to-be published book into the affair. He said Musharraf did not provide adequate security for the former prime minister.

He quotes a former Pakistani diplomat who said Musharraf taunted Bhutto, allegedly telling her: "I'll only protect you if you are nice to me."

Musharraf is a hate figure within the judiciary and may struggle to receive a fair trial. The enmity dates from 2007 when top judges were put under house arrest after he declared emergency rule - the subject of another of the three cases against him, for which he was formally indicted in June.

The third case relates to the killing during a military operation of a tribal leader in the insurgency wracked province of Baluchistan called Akbar Khan Bugti in 2006.

Potentially far more troubling for Musharraf was the government announcement in June that the former president should be tried for treason, a capital offence.

Only the government can pursue a treason trial and many analysts had assumed newly elected prime minister Nawaz Sharif would avoid picking a fight with the powerful army that does not want to see one of its former leaders imprisoned or executed.