ISLAMABAD, Pakistan — Pakistani forces captured and critically wounded a senior Taliban militant yesterday, 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 American-backed campaign against the Taliban and Al Qaeda, though it also demonstrated that militant chiefs operate inside Pakistan despite its deployment of 100,000 troops along the border.

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

The Pakistani army said Mr. 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.

Major General Athar Abbas, the army spokesman, denied initial reports that Mr. Dadullah had died. “Dadullah was arrested alive, but he is critically wounded,” General 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 Mr. 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 the Taliban’s 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 February 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.