Fighting has escalated in northern Afghanistan as the United States prepares for military strikes against the Taliban unless they hand over Osama bin Laden, chief suspect in the Sept. 11 terrorist attacks in New York and Washington that killed thousands.

In the strategic Panjshir Valley 45 miles north of Kabul, heavy exchanges of mortar and artillery fire could be heard shortly before dawn Monday.

Speaking in the Panjshir Valley, Rakhmat Ramazan, a spokesman for the northern alliance, said Taliban troops pounded opposition positions with artillery starting late Sunday. Raising his voice to be heard over the thundering explosions, Ramazan told reporters the opposition was preparing a counterattack.

Heavy fighting was also reported late Sunday and early Monday in Balkh province, 175 miles northwest of the valley. Another opposition spokesman, Mohammed Ashraf Nadeem, said his forces were attacking the Taliban to try to win control of the district of Aq Kupruk.

Battles has been under way in Balkh and the bordering province of Samangan for days. The Taliban have admitted losing control of the Balkh provincial village of Zari, 60 miles south of Mazar-e-Sherif. Loss of the village threatens Taliban control of a strategic highway linking central Afghanistan with Uzbekistan to the north.

It is difficult to confirm claims by the two sides. The Taliban have ordered foreigners, including journalists, U.N. officials and aid workers, to leave the country.

The Taliban control more than 90 percent of Afghan territory. But the northern-based opposition alliance has stepped up its offensives since the suicide attacks in New York and Washington and the Sept. 15 death of its leader, Ahmed Shah Massood, who died from wounds suffered in a suicide bombing.

In recent days, the United States has increased its contacts with the opposition alliance in preparation for a possible assault on the Taliban, bin Laden and his training camps. The Taliban have rejected U.S. demands to hand over bin Laden and close his training camps, which Washington considers the focal point for the worldwide Al-Qaeda terrorist network.

On Sunday, Taliban officials said they have been unable to locate bin Laden. U.S. officials dismissed the claim, saying they believe the Taliban know exactly where bin Laden is.

In Kabul, a top Taliban official said Monday that America has no right to attack Afghanistan but that the militia has all the weapons and ammunition it needs to fight off U.S. ground or air assaults.

"Around 300,000 experienced mujahedeen (holy warriors) are guarding the borders and all other important places in Afghanistan," Mullah Obaidullah Akhund, the Taliban defense minister, said in a statement. He also said many Taliban supporters are joining the militia.