Suspected Islamic militants fatally shot eight tribal leaders involved in efforts to broker a cease-fire between security forces and insurgents in Pakistan's volatile northwest, authorities said Monday.

Meanwhile, a homicide attacker in a pickup truck detonated a bomb near a guest house where military officers were staying Monday, also in the country's northwest, wounding five people, the military said.

The tribal leaders were killed in separate attacks late Sunday and early Monday in South Waziristan, a mountainous region close to Afghanistan where Al Qaeda and Taliban militants are known to operate, a security official and the military said in a statement.

The suspected insurgents killed three of the men in a market in Wana, the region's main town, while the other five were killed in attacks on their homes, the security official said. The men were scheduled to meet each other on Monday in Wana to discuss the negotiations, the official said, speaking on condition of anonymity because he was not authorized to talk to media.

Pakistan is an ally in the U.S. War on Terror, and its security forces have fought intense battles with militants in South Waziristan. Although the government has encouraged moderate tribal elders to broker a cease-fire in the region, there has been little sign of success.

In the homicide attack, the bomber blew himself up when he was stopped by soldiers at a checkpoint, wounding three soldiers and two civilians, the military said in a statement.

The attack happened in the town of Kabal in the Swat region, a former tourist destination where security forces have been battling loyalists of a pro-Taliban cleric. Swat is about 175 miles north of South Waziristan.

The Pakistan-Afghanistan border area has long been considered a likely hiding place for Al Qaeda leader Usama bin Laden and his top deputy Ayman al-Zawahri, and the U.S. has pressured the government of President Pervez Musharraf to crack down on militants operating in the area.

On Sunday, Pakistan reiterated that it will not let American forces hunt Al Qaeda and Taliban militants on its soil, after a report in The New York Times said that the Bush administration was considering expanding U.S. military and intelligence operations into Pakistan's tribal regions.

The Pakistani government also has blamed Baitullah Mehsud, a South Waziristan-based militant leader with links to Al Qaeda, in the Dec. 27 assassination of opposition leader Benazir Bhutto. Mehsud has reportedly denied involvement, and many Bhutto backers claim elements within the government played a role in her killing.

About 2,000 supporters of the All Parties Democratic Movement, a coalition of small opposition parties that have called for a boycott of upcoming parliamentary elections, held a protest in Chaman near the Afghan border, chanting "Arrest the killers of Benazir Bhutto" and "Death to fraudulent elections."

Protesters also denounced the government for a scarcity of flour and electricity.

Rallies were scheduled for later Monday across the country, said Shahid Shamsi, a spokesman for Jamaat-e-Islami, Pakistan's largest Islamic group, which is also part of the anti-Musharraf coalition.