Roadside bombs struck two vehicles in Pakistan's volatile northwest Sunday, killing a former irrigation minister and three others in one attack and two anti-Taliban tribal elders in the other.

Public officials and private citizens combatting the growing Taliban-led insurgency in Pakistan have been frequent targets in a wave of violence that has killed more than 600 people in the past two-and-a-half months.

A single attack two days ago killed nearly 100 people when a homicide car bomber struck a sports event near a meeting of tribesmen who supervise an anti-Taliban militia near Pakistan's South Waziristan tribal area.

The Pakistani army invaded South Waziristan in mid-October in an attempt to neutralize the Pakistani Taliban's main stronghold in the country, but many militants fled the offensive and have been launching attacks elsewhere in the northwest.

The Pakistani government has pledged it will persevere despite the violence but has resisted U.S. calls to expand its offensive to target militants launching cross-border attacks against coalition troops in Afghanistan.

The U.S. has responded by increasing drone missile strikes in Pakistan's tribal areas, including one such suspected attack Sunday in North Waziristan that killed at least two people, according to intelligence officials.

Hours earlier, a roadside bomb struck a vehicle in the Hangu district of North West Frontier Province, killing former Irrigation Minister Ghaniur Rehman, his two guards and his driver, said district police chief Abdur Rasheed. Two police officers accompanying the former minister were wounded in the attack, he said.

Rehman was affiliated with the Pakistan People's Party (Sherpao group) headed by former Interior Minister Aftab Khan Sherpao, who has survived two homicide bomb attacks.

The attack came after a roadside bomb struck a vehicle carrying anti-Taliban elders in the Bajur tribal area, killing two and critically wounding four others, said local official Naseeb Shah. The six men were working to set up an anti-Taliban militia in Bajur, a militant stronghold near the Afghan border, said Shah.

The men were on their way to meet local officials in the main town of Khar when the remote-controlled device detonated, Shah said. The blast occurred near Kassai, about 17 miles (28 kilometers) northeast of Khar, he said.

The Pakistani military carried out an anti-Taliban offensive in Bajur in 2008 and 2009 that it declared a success. But the militants have maintained their presence, and violence has flared in the region since then.

The bullet-riddled bodies of a man and a woman were found in the Mamund area of Bajur on Sunday with a note saying they were guilty of violating Islamic law, local official Faromosh Khan said.

Militants have stepped up attacks in other parts of the northwest as well in apparent retaliation for the recent South Waziristan offensive.

The homicide car bombing in the northwest village of Shah Hasan Khel near South Waziristan that killed 96 people on New Year's Day was one of the deadliest attacks since the army launched the operation.

Police believe the attacker meant to detonate his 550 pounds (250 kilograms) of explosives at the meeting of anti-Taliban tribesman. Instead, the blast went off at a nearby outdoor volleyball court, leveling some three dozen mud-brick homes and covering the village in Lakki Marwat district with dust, smoke and the smell of burning flesh.

None of the elders meeting at the time of the attack were killed, and they insisted residents will keep defying the Taliban.

Ameer Haider Khan Hoti, the chief minister of Northwest Frontier Province, where Lakki Marwat is located, said recent military operations had put militants on the defensive and they were lashing out.

"They are running and they are targeting citizens," Hoti told reporters after visiting victims of the bombing being treated at a hospital in the provincial capital of Peshawar.

"Militants and militancy is a cancer, and our struggle against it will continue until it vanishes completely," he said.

But the Pakistani government has resisted U.S. calls to expand its military offensive, saying it has its hands full fighting militants waging war against the state.

Washington's covert drone program targeting militants in Pakistan's tribal areas is one way of taking the battle into its own hands.

The suspected U.S. drone missile strike that killed two men Sunday near the town of Mir Ali in North Waziristan targeted the house of a well-known tribesman, said intelligence officials, speaking on condition of anonymity because they were not authorized to talk to the media.

It was unclear if the two killed were militants or civilians.

U.S. officials rarely discuss the missile strikes, and although Pakistan's government publicly condemns them as violations of its sovereignty, many analysts believe the two countries have a secret deal allowing them.