Pakistan ordered its army to go after the country's top Taliban commander, a feared Al Qaeda-allied militant whose remote stronghold could prove a difficult test for troops but whose demise would remove a major threat to the country's stability.

The announcement Sunday of the operation in South Waziristan, rumored for weeks, came hours after a suspected U.S. missile strike killed five alleged militants there. The move will likely please Washington, which wants Pakistan to eliminate safe havens for militants leaving Afghanistan and which considers South Waziristan a particularly troublesome hideout for Al Qaeda.

Owais Ghani, the governor of North West Frontier Province, told reporters in Islamabad late Sunday that the government felt it had no choice but to resort to force against Pakistani Taliban chief Baitullah Mehsud and his network. Past army action in the region had usually faltered or ended in truces, strengthening the militants.

"Baitullah Mehsud is the root cause of all evils," Ghani said, noting a slew of suicide bombings that have shaken Pakistan in recent days. "The government has decided that to secure the innocent citizens from terrorists, a meaningful, durable and complete action is to be taken."

Ghani suggested the operation has already begun, though the military has insisted its recent attacks on militants in South Waziristan were retaliatory, not the launch of a new offensive. Two intelligence officials said the army and Taliban were fighting in the Spinkai Raghzai area of South Waziristan as the governor made the announcement.

Army spokesman Maj. Gen. Athar Abbas told The Associated Press late Sunday: "The government has made the announcement. We will give a comment after evaluating the orders."

South Waziristan, part of Pakistan's semiautonomous tribal belt, is a rumored hide-out of Al Qaeda chief Usama bin Laden. As the military has pursued a separate offensive against Taliban fighters in the northwest's Swat Valley, observers have noted that the Taliban will not be defeated in Pakistan unless they lose their tribal sanctuaries.

The U.S. has frequently targeted South Waziristan with missile strikes. The suspected strike Sunday hit three vehicles and killed five suspected militants. Two Pakistani intelligence officials confirmed the attack on condition of anonymity because they were not authorized to speak to the media.

Neighboring North Waziristan, another militant stronghold and target for U.S. missiles, may also fall under the new Pakistani offensive at some point.

Mehsud is believed to pose a serious internal threat to the Pakistani government, and has been blamed for the killing of former Prime Minister Benazir Bhutto, though he has denied that accusation. The Taliban chief also has been linked to attacks on both sides of the Afghanistan-Pakistan border, though he is believed to have operated primarily in Pakistan.

In many ways, a full-scale battle in South Waziristan will be a harder fight than in Swat, where the army claims to have killed hundreds of militants over the past six weeks.

One reason is that the tribal region's porous border with Afghanistan could make it easier for militants to escape to the other side. Because of the tribal belt's semiautonomous nature, the government has long had limited influence, allowing militants to become deeply entrenched.

A new offensive could also mean more displaced civilians in Pakistan, already struggling to deal with more than 2 million who fled their homes in Swat and surrounding districts.

Pakistan's decision comes as public opinion has shifted against the Taliban, who have been blamed or have claimed responsibility for a series of bloody attacks in recent weeks, including one that killed a prominent anti-Taliban cleric and another that devastated a luxury hotel in Peshawar.

On Sunday, a bomb rocked a market in the northwestern town of Dera Ismail Khan, while officials said clashes between the Taliban and security forces killed at least 20 militants in a tribal area supposedly cleared of insurgents months ago.

Government official Inayat Ullah said 11 to 13 pounds of explosives were planted in a fruit vendor's hand-pulled cart in the market. Police official Mohammad Iqbal put the death toll at nine, with 20 wounded.

At a hospital where some of the wounded were taken, cries punctured the air.

"It was crowded there when something big exploded," said 30-year-old Ilyas Ahmad, whose legs were wounded. "It was a big noise. Everybody was crying. Bodies were lying there. People were lying around blood."

A Taliban commander, Qari Hussain Ahmad, blamed the blast on Pakistani intelligence agencies, saying the government was carrying out such acts to legitimize an operation in Waziristan.

"They want to malign us. They want to use killings of innocent citizens against us," Hussain told The Associated Press by phone from an undisclosed location.

Fighting on multiple fronts could tax the army's ability to hold regions once it says it has cleared them. The latest clashes in the Bajur tribal region underscored that.

Bajur was the main theater of operations against the militants before Swat. After some six months of fighting, the army said in February that the Taliban there had been defeated. But there have been occasional reports since then of ongoing militant activity.

Pakistani forces used jets, helicopters and artillery to pound suspected Taliban hide-outs in Bajur over the weekend.

Zakir Hussain Afridi, the top government official for Bajur, said the fighting was in the Charmang valley, a stretch he described as largely under Taliban control. Jamil Khan, his deputy, put the militant death toll at 20 since Friday.