BAGHLAN-I-JADID, Afghanistan - Taliban insurgents have taken over parts of two northern provinces from which they were driven in 2001, threatening to disrupt NATO's new supply route from Central Asia and expand a war that has largely been confined to Afghanistan's southern half, U.S. and Afghan officials said.

Insurgents operating in Baghlan province along the highway from Tajikistan launched coordinated attacks during the Aug. 20 presidential election, killing the district police chief and a civilian, while losing a dozen of their own men, local officials said. It was the worst bloodshed reported in the country that day.

The violence has been on the rise in recent months, however, as the Taliban and foreign fighters linked to al-Qaeda have staged hit-and-run attacks, bombings, and rocket strikes on German, Belgian, and Hungarian forces in Baghlan and the neighboring province of Kunduz.

The insurgents now control three Pashtun-dominated districts in Kunduz and Baghlan-i-Jadid, a foothold in a region that was long considered safe. With a force estimated at 300 to 600 hard-core fighters, they operate checkpoints at night on the highway to the north, now a major supply route, local officials said, and are extorting money, food, and lodging from villagers.

"The Taliban want to show the world that not only can they make chaos in southern Afghanistan, but in every part of Afghanistan," Baghlan Gov. Mohammad Akbar Barekzai said. "This is a big problem. We don't have sufficient forces here."

For U.S. commanders, whose stretched forces have been unable to pacify the south and are taking record casualties, it's another looming problem.

"What can we do to mitigate the risk? It's a question of means," said a senior U.S. defense official, who requested anonymity because he wasn't authorized to speak publicly. "Clearly, the main effort is in the south. But we can't allow other areas of the country to be destabilized."

The official said he has begun discouraging Western aid workers from visiting projects in those areas.

The growing Taliban presence also threatens to aggravate long-standing tensions into violence between the region's Pashtuns - the ethnic group that dominates the Taliban - and Tajiks.

Many Pashtuns, descendants of settlers from southern Afghanistan awarded lands in the north in the early 20th century, supported the Taliban's rule of the 1990s, while many Tajiks fought against the religious militia.

Another potential danger is that foreign extremists linked to al-Qaeda could use Taliban sanctuaries in the north to stir up trouble in the adjacent former Soviet republics of Uzbekistan and Tajikistan, whose authoritarian rulers have brutalized their Muslim populations.

"Al-Qaeda wants to have a base there," said retired Gen. Hillaluddin Hillal, a parliamentarian from Baghlan. "Al-Qaeda's support is behind them [the Taliban]. Al-Qaeda has an interest in Central Asia."

A senior U.S. intelligence official confirmed that Arabs, Chechens, Uzbeks, and Pakistanis affiliated with al-Qaeda have been making their way into Baghlan and Kunduz from Pakistan's tribal areas.

The new NATO supply link, established after Pakistani insurgents began attacking the main logistics route from the Pakistani port of Karachi, consists of two roads, one from Uzbekistan and one from Tajikistan. After merging in Baghlan province outside the city of Pul-i-Khumri, the highway runs south through the towering Hindu Kush mountains to the main U.S. base at Bagram and to Kabul.

"The concern is if we don't stunt the [Taliban] growth, it could cause problems with our northern distribution network," said the senior intelligence official, who asked not to be further identified because he wasn't authorized to speak publicly. Citing the Taliban leader Mullah Mohammed Omar, he continued: "A couple of years ago, Mullah Omar said, 'We need to open up new fronts in the north and cause a dissipation of [U.S.] resources.' To a degree, it's working."