ISLAMABAD, Pakistan — Pakistani forces captured and critically wounded a senior Taliban militant on Monday, the second successful targeting in two weeks of a terror suspect as the government faced growing Western pressure to crack down on cross-border attacks into Afghanistan.

But in a reminder of the growing militant threat destabilizing Pakistan, a suicide bomb wounded a candidate and killed seven others as he campaigned for next week's parliamentary elections. Also, Pakistan's ambassador to Afghanistan was missing and feared kidnapped as he traveled in a volatile Pakistani tribal region.

The arrest of Mansoor Dadullah, brother of slain Taliban military commander Mullah Dadullah, was a boost for the U.S.-backed campaign against the Taliban and al-Qaida, though it also demonstrated that militant chiefs operate inside Pakistan despite its deployment of 100,000 troops along the border.

It followed a Jan. 29 U.S. missile strike on a militant hideout in the northwestern tribal belt that killed Abu Laith al-Libi, a top al-Qaida commander in Afghanistan.

Mansoor Dadullah was caught in the southwestern province of Baluchistan, but there was some confusion over exactly how and where.

The Pakistani army said Dadullah was wounded along with five militant associates in a firefight with security forces near a village in Qila Saifullah district after they sneaked across the border from Afghanistan. But local intelligence officials placed the clash in neighboring Zhob district, describing it as a raid launched by security forces against the militants hiding at a religious seminary.

Maj. Gen. Athar Abbas, the army spokesman, denied initial reports that Dadullah had died. "Dadullah was arrested alive, but he is critically wounded," Abbas said.

The intelligence officials, who spoke on condition of anonymity because they were not authorized to speak to journalists, said all the suspects were moved by helicopter from Zhob. It was not clear where they were taken or whether Dadullah would be handed over to Afghan authorities.

Western and Afghan officials have long said Baluchistan is used by the Taliban as a base for its operations inside southern Afghanistan. Pakistan has repeatedly denied that Taliban supreme leader Mullah Omar is hiding in the Baluchistan capital, Quetta.

In the past year, Pakistani security forces have struggled to contain a wave of attacks as Taliban militants have expanded their influence, particularly challenging the government's control of the lawless northwest.

In the latest violence, a suicide attack in the North Waziristan tribal area wounded an independent candidate running in the Feb. 18 parliamentary elections and killed at least seven other people.

Nisar Ali Khan's candidacy was informally supported by the Awami National Party, a secular group of ethnic Pashtuns seen as opposed to the Taliban. Afrasiab Khattak, the party's provincial chief, said its top leader in Waziristan was among the dead.

On Saturday, a suicide bomber struck a gathering of Awami party supporters in the northwestern town of Charsadda, killing at least 27 people.

Underscoring the insecurity of the border region, Pakistan's ambassador to Afghanistan, Tariq Azizuddin, was reported missing and feared kidnapped as he headed Monday by road to Kabul.

Government-run Pakistan Television said Azizuddin went missing in the tribal region of Khyber, through which travelers must pass to reach the main international checkpoint between northwestern Pakistan and Afghanistan. Officials said security agencies were searching for him.

The threat by Islamic extremists is among a range of crises battering this nuclear-armed country as it prepares for next week's elections. The campaign has been overshadowed by militant attacks, particularly the Dec. 27 assassination of opposition leader Benazir Bhutto, whose populist party is tipped to win the polls.

With the election only days away, a survey released Monday by a U.S.-funded group with ties to the Republican Party found that support for President Pervez Musharraf had plunged to an all-time low and that opposition parties appeared poised to score a landslide victory.

The survey by the International Republican Institute found that 75 percent of the respondents wanted Musharraf to resign, and only 15 percent approved of his performance. Only 9 percent believed Pakistan should cooperate with the United States in the war against terror, the survey said.

The poll of 3,845 adults from urban and rural areas was conducted Jan. 19-29 and has a margin of error of plus or minus about two percentage points.