ISLAMABAD - Pakistan ordered its army to go after the country's top Taliban commander, a feared militant whose remote stronghold could prove a difficult test for troops but whose demise would be a major blow to the insurgencies here and in Afghanistan.

The announcement yesterday 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 considers the tribal region a particularly troublesome hide-out for al Qaeda and Taliban fighters implicated in attacks on U.S. troops in Afghanistan.

Owais Ghani, the governor of North West Frontier Province, told reporters in Islamabad late yesterday 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.

South Waziristan, part of Pakistan's semiautonomous tribal belt, is a rumored hide-out of al Qaeda chief Osama 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 yesterday 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. *