Thousands of troops fanned out across Pakistan on Tuesday to bolster security ahead of next week's parliamentary elections, with senior military officials pledging they would not manipulate the vote.

At least nine people were wounded Tuesday in a bomb blast near the office of a candidate in the southwestern province of Baluchistan — the latest in a string of attacks that have marred the campaign.

"The bomb was planted in a bicycle parked near the election office where Sardar Aslam Bizenjo was preparing to address a press conference," said Hamid Shakeel, the police chief in Khuzdar, 185 miles south of Quetta.

The candidate was unhurt and there were no immediate claims of responsibility.

There are concerns that militants could launch attacks during the Feb. 18 vote, seen as key to Pakistan's transition to democracy after eight years of military rule under President Pervez Musharraf, a key U.S. ally in its war against terrorism.

But the main fear is a major outbreak of political violence if there are allegations of vote rigging.

The army earlier said it would only deploy forces if it was asked to do so by civilian authorities.

Interior Ministry spokesman Jawed Iqbal Cheema said provincial officials had asked for the troops to help maintain peace and order during the elections, and promised that none would be stationed at voting stations.

Arif Ahmad Khan, home secretary in the southern province of Sindh, said about 24,000 troops would be deployed there alone.

Furqan Bahadur, home secretary in Baluchistan, said security forces there would be placed on standby, responding only if violence flared.

Underscoring the security threat, dozens of people were killed in a suicide bombing over the weekend and an attack Monday wounded a candidate while he was campaigning.

Security forces also were searching for Pakistan's ambassador to Afghanistan, who was missing and feared kidnapped as he traveled in a volatile Pakistani tribal region.

The security threat has heightened at a time when public support for Musharraf has plunged to an all-time low. Opposition parties loyal to the late Benazir Bhutto and former Prime Minister Nawaz Sharif appear poised for a landslide victory, recent polls showed.

Musharraf is not a candidate but needs a commanding majority in the new parliament to block any moves to impeach him.

He is grappling with rising Islamic extremism, especially in the northwestern regions bordering Afghanistan.

He also faces political dissent following his move last year to oust Supreme Court judges seen as a challenge to his rule.

The deposed chief justice, Iftikhar Mohammed Chaudhry, and his family remain under house arrest in the capital, Islamabad. Several other senior independence-minded judges are also restricted to their homes.

"Days before Pakistan goes to the polls, its lawful chief justice and his children remain under illegal house arrest, as do many lawyers who would likely challenge election rigging in the courts," said Brad Adams, Asia director at the New York-based Human Rights Watch.

"Musharraf's systematic destruction of legal institutions has seriously compromised the upcoming elections," he said.