Entrenched rebels kept advancing Russian forces out of the coveted center of Grozny, Chechnya's capital, as blazing oil wells on the city's southern edge sent columns of smoke billowing into the air. The Russians pushed on with their offensive to seize Grozny, though commanders said they were moving cautiously because of mines. Russian artillery battered the city from all sides. At least 15 oil wells went up in flames. But there was no sign in central Grozny of Russian forces or the pro-Moscow Chechen militia.