Russians Claim to Repel Separatists

GUDERMES, Russia — Federal forces claimed Friday to have the upper hand in street fighting in Grozny, the Chechen capital, even after rebels demonstrated their freedom of movement by mounting surprise attacks from the rear using underground passages.

Acting President Vladimir V. Putin warned that with battlefield success came an increasing danger of Chechen-organized terrorist groups.

“The danger of terrorist acts is growing and will exist until we finish off the bandits in Chechnya,” he told Interior Ministry officials.

The surprise attacks Thursday came after days of street combat in which Russian forces failed to capture the center of Grozny. The rebels infiltrated Russian positions through underground pipes, which they continue to control. Both sides suffered losses, the military said.