Pakistani security forces fought street battles with Taliban militants in the Swat Valley's main urban center, a critical phase in the effort to wrest the northwest region near Afghanistan out of insurgent hands.

Army spokesman Maj. Gen. Athar Abbas warned Saturday the operation in Mingora town could be "painfully slow," noting some 10,000 to 20,000 civilians are still trapped there. The fight also could prove a major test for a military more geared toward conventional warfare on plains than bloody urban battles.

The military operation in Swat and surrounding districts has strong support from Washington, which wants Pakistan to root out insurgents who use its territory to plan attacks on U.S. troops in Afghanistan. For now, it appears to have broad public support in Pakistan as well.

Abbas said 17 suspected militants had been killed in the past 24 hours of the operation in the valley. He said another major town, Matta, was cleared of militants. But some 1,500 to 2,000 insurgents remained in Swat - hard-core fighters, he said.

Mingora, which normally has at least 375,000 residents, is a major commercial center for the valley, one the military had been preparing to enter for several days.

"The terrorists are going to use (civilians) as human shields. They are going to make them hostage, so we are moving very carefully," Abbas said. "The pace of the operation will be painfully slow. So keep patient. But the operation has started and, God willing, we are going to take it to the logical conclusion."

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