They also heard 10 powerful explosions Wednesday evening near the Afghan village of Kalai-Zal, about 5-6 miles from the border, military observers with the border guards said.

They did not speculate on the cause, but intense combat has been reported in the area between the Taliban militia, which controls about 90 percent of the Afghanistan, and the northern alliance, which controls a sliver of the north.

Northern alliance tanks on Thursday shelled Taliban positions near the village of Zardkamar, near the Tajik border, the border guards said.

The sound of heavy artillery, tanks and planes could be heard in the wee hours Thursday near the village of Kachakum, 1.5 miles from the junction of the Afghan, Tajik and Uzbek borders, and it continued into Thursday afternoon, the press service said.

The village is north of Mazar-e-Sharif, the largest city in northern Afghanistan. Taking Mazar-e-Sharif would enable the opposition to consolidate its grip on the small area it controls in the north, since the town controls routes running east to west and linking pockets of the northern alliance's strength.

The northern alliance said Monday that it was preparing a major offensive that would target Mazar-e-Sharif, among other key cities. Capturing the city could give alliance fighters their first tangible success.

Russia has about 25,000 troops based in Tajikistan to help stem the flow of smuggled drugs and weapons into Central Asia. Its troops are also seen as a bulwark against any attempted Taliban incursions into the former Soviet republic.