The shift is a dangerous one for Russia, which hopes to prevent high casualties among its soldiers.

With Russian air and artillery attacks pounding Grozny, federal troops seized the final road into the city over the weekend and their commanders announced that it was under a full blockade.

Russian troops have met relatively little opposition during the first two months of the military campaign, but rebels have begun putting up more of a fight as the Russians move toward Grozny, a Russian military spokesman said Sunday.

Col. Gennady Alyokhin warned that Chechnya's "illegal armed formations were increasingly using guerrilla methods of warfare."

On the outskirts of the capital, Russian forces said their troops inflicted heavy losses on rebels by capturing a network of defensive bunkers.

"Our reconnaissance feigned an attack and drew fire. The rebels lost about 50 men," a Russian general said.

Most Russians have supported the Chechen campaign, but if the military opts to storm Grozny, heavy losses among Russian troops are likely. Such losses could provoke the kind of public indignation that met the previous war in 1994-96 -- a development that both the military and the government are anxious to avoid.

Russian commanders say they do not intend to take Grozny with ground troops. However air strikes and artillery attacks alone are unlikely to dislodge thousands of rebel fighters in the city.

A rebel Web site said on Sunday that the battle for Grozny had begun. It acknowledged that Russian troops controlled all roads out of the city, but said Chechen fighters could skirt Russian positions and were reinforcing Grozny's defenses. The rebels say they have adequate food and ammunition supplies.

Russian officials have said their next target will be Urus Martan, a town 15 kilometers (10 miles) south of the capital where rebels have put up their stiffest resistance yet.

Grozny mayor Lecha Dudayev warned Sunday that lack of transportation would prevent civilians from using a proposed safe-passage corridor. The Russian military plan to open a pathway on Monday to move mostly the elderly and infirm to the Russian-controlled north of the territory. Dudayev said the Grozny residents would have to cover up to 20 kilometers (12.5 miles) on foot, Interfax news service reported.

Deaths and suffering among Chechen civilians have brought strong criticism from the West. Russia's campaign has forced approximately 200,000 people to seek shelter in neighboring Russian republics where they face winter shortages of food, fuel and other basic items.

In neighboring Ingushetia, refugees have scrambled to find living quarters. In the village of Mozdok, 40 Chechens took shelter in a cemetery, sleeping in a large shed where rites for the dead are performed.

"It was terrible at first. You come out and there are graves everywhere. But it was worse at home," one woman said.

There were reports of a civilian massacre over the weekend. Chechen refugees who fled Grozny said masked Russian soldiers at a checkpoint had opened fire on their caravan at point blank range, killing 40 people. Russian military officials denied the allegations<