Pervez Musharraf was Tuesday disqualified from contesting Pakistani elections next month, crushing his ambition to 'save' the troubled nuclear-armed country just weeks after his return from exile.

Pakistan goes to the polls on May 11, marking the first time a civilian government has handed over power at the ballot box after completing a full term in office in a country used to extended periods of military rule.

The Pakistan election campaign has got off to a lacklustre start and been marred by violence and Taliban threats. On Tuesday, a bomb targeted a convoy of the main opposition Pakistan Muslim League-N (PMLN) party, killing four people.

Election officials disqualified Musharraf just one day after he unveiled his All Pakistan Muslim League (APML) party manifesto at a press conference overshadowed by questions about a series of legal cases dating back to his nine years in power.

The retired general is on bail over the 2007 killing of former prime minister Benazir Bhutto and the 2006 death of a rebel leader from the region of Baluchistan, and for sacking judges when he imposed emergency rule in 2007.

But he told reporters Monday: "The only thing in my heart was to save Pakistan and now I am here I have the same commitment, that I will save Pakistan."

The Taliban threatened to assassinate him on the eve of his return to Pakistan on March 24, where he was welcomed by only a few hundred ardent supporters.

The 69-year-old applied to run for parliament in four seats but was rejected immediately from all but the northern district of Chitral, on the Afghan border.

Lawyers appealed against his approval in Chitral and on Tuesday a court official said Musharraf's nomination had been thrown out on the grounds that he violated the constitution in 2007.

Musharraf's team have vowed to appeal against the decision in the Supreme Court, which is also hearing a separate petition from lawyers demanding that Musharraf face trial for treason dating back to his 1999-2008 rule.

Lawyer Ahmed Raza Kasuri said the decision was an insult to "an internationally known person" and would show the world "what democracy we have".

"Let us see what the Supreme Court decides. We are hopeful we will get justice," close Musharraf aide and APML candidate in Islamabad, Mohammad Amjad, told AFP, denying that the decision would have any impact on the party's campaign.

Musharraf's main rival in Chitral told AFP that he asked for him to be disqualified for violating the constitution, killing Bhutto, seizing power in 1999 and raiding an extremist mosque in Islamabad in 2007.

"I also requested the tribunal to disqualify him on grounds of killing Akbar Bugti and allowing America to invade Afghanistan," Maulana Abdul Akbar Chitrali, a candidate for the religious Jamaat-e-Islami party.

Tuesday's attack in the Khuzdar district of southwestern province Baluchistan was the third deadly attack on politicians or political parties in as many days.

Sanaullah Zehri, head of the PMLN in Baluchistan, survived but his son, brother, nephew and their guard were all killed, officials said.

"An improvised explosive device went off as Zehri, leading a convoy of more than 20 vehicles, left his home to campaign in Khuzdar," provincial home secretary Akbar Durrani told AFP.

There was no immediate claim of responsibility, but the Pakistani Taliban have said they were behind two deadly roadside bomb attacks in the northwest on Sunday.

Zehri survived a murder attempt two years ago that was claimed by the rebel Baluch Liberation Front.

In Peshawar, a candidate for the Pakistan People's Party (PPP) which led the national government from 2008 told AFP he escaped a grenade attack at his home unhurt on Tuesday.

On Monday gunmen killed two election campaigners for an independent candidate running in the lawless northwestern tribal regions, a day after a roadside bomb in the Swat valley killed a local leader of the Awami National Party (ANP).

On Thursday a grocer standing in the polls for the secular Muttahida Qaumi Movement (MQM) was shot dead in the southern city of Hyderabad, an attack also claimed by the Taliban.

Pakistan's caretaker interim prime minister Mir Hazar Khan Khoso ordered an immediate tightening of security for all candidates in the wake of that shooting.