Image copyright AFP Image caption Pervez Musharraf returned from self-imposed exile to contest elections last month

Pakistan's former military leader Pervez Musharraf has been barred from standing in general elections in May.

An election tribunal disqualified him from running in Chitral in the north-west. Earlier, he failed in an attempt to stand in three other seats.

Mr Musharraf's lawyer says he plans to file an appeal with the Supreme Court.

Meanwhile, at least four people were killed in an attack on a convoy of the main opposition PML-N party in the south-western province of Balochistan.

Pervez Musharraf returned from self-imposed exile in Dubai and London last month saying he wanted to save Pakistan, hoping to lead his All Pakistan Muslim League (APML) party into the general election next month.

Legal battles

On his return, Mr Musharraf submitted papers to contest the poll from Karachi, Islamabad, Kasur and Chitral.

Analysis It has been a bad day for former military ruler Pervez Musharraf. Weeks after he returned to stand in the elections, a tribunal has ruled he cannot be a candidate. Apparently, the country's powerful military, of which he was the head until 2007, has not intervened to prevent his political fall. He can appeal against the decision in the Supreme Court, but it is headed by a judge he unsuccessfully tried to sack when he was president. He has other problems as well. He has been struggling to avoid arrest in two murder cases, and the Supreme Court is considering whether he should be tried for treason. He has already been barred from leaving the country, and is also a target for the Pakistani Taliban. But while his future appears increasingly bleak, few believe the military would allow a former chief to be thrown in jail or assassinated by militants.

While Mr Musharraf was given initial approval to run in Chitral, he was rejected in the remaining constituencies.

His opponents later filed an appeal against the decision to approve his candidacy in Chitral on the grounds that he had violated Pakistan's constitution when he imposed emergency rule in 2007.

The former general seized power in a military coup in 1999 and remained in office until 2008 when his supporters were defeated in parliamentary elections. Under threat of impeachment, he left the country.

He is already embroiled in a series of legal battles and has been attempting to stave off arrest and a bid to try him for treason.

He is facing a number of charges related to his time in office with court proceedings over the killing of Benazir Bhutto in 2007 and a tribal leader from Balochistan.

He has described the cases against him as "baseless" and politically motivated.

In addition to his legal and political woes, the Pakistani Taliban have vowed to target him with a squad of suicide bombers.

"His paper has been rejected by the high court. We will file an appeal in the Supreme Court," Mr Musharraf's lawyer Ahmed Raza Kasuri told AFP.

But after the tribunal's latest decision and if an appeal fails, Mr Musharraf will be ruled out of the running.

Separatist threats

There was no immediate claim for the attack in Balochistan. Correspondents say the area where the attack took place has no Taliban presence and is known to be a hotbed of separatist rebel activity.

The BBC's M Ilyas Khan says that militant threats against secular politicians and parties, such as the ruling PPP and ANP, are hampering their election campaigns.

The brother, son and nephew of the leader of the PML-N party, Sardar Sanaullah Zehri, were killed in the bomb attack in Kuzdar in Balochistan, according to officials.

Mr Zehri narrowly escaped an earlier IED attack in Kalat area of Balochistan in October 2011. The attack was claimed by an armed separatist group, the Balochistan Liberation Front (BLF).

Most election violence in Pakistan takes place in the north-west of the country and secular parties such as the ANP, in power in Khyber Pakhtunkhwa province, and the ruling PPP have borne the brunt of such attacks.