CHERMEN, Russia - Thousands of troops poured into a southern Russian city today, chasing suspected Chechen rebels who set fire to police and government buildings and killed at least 48 people in brazen overnight attacks.

An official with the interior ministry for the province of Ingushetia said 48 people been killed, including 18 police, but the Interfax news agency later quoted President Vladimir Putin's envoy to the region as saying 47 police and an unknown number of civilians died.

Three high-ranking regional officials were among the dead in the militants' foray into Ingushetia.

The attacks underscored the Russian military's failure to defeat separatists in neighboring Chechnya after five years of fighting, and raised new fears of spreading violence in southern Russia.

Putin ordered authorities "to find and destroy" the militants whose raid came amid preparations for an August election to replace Kremlin-backed Chechen President Akhmad Kadyrov, killed last month in a bomb attack. Kadyrov's death was seen as a significant blow to Putin's efforts to bring some stability to Chechnya, devastated by two wars since the 1990s.

Shortly before midnight Monday, about 100 fighters armed with grenades and rocket launchers seized the regional Interior Ministry in Nazran, the largest city in Ingushetia and attacked border guard posts there. They also attacked posts in two villages near the border with Chechnya, Karabulak and Yandare, regional emergency officials said.

Authorities sent in reinforcements shortly after dawn today, with a long column of armored personnel carriers, army trucks and troops moving into Nazran through the border village of Chermen in neighboring North Ossetia.

By midmorning, most of the militants had fled into the thick forests on the border of Ingushetia and Chechnya, authorities said. Ingush President Murat Zyazikov told the Interfax news agency that a large number of weapons and ammunition were missing from police depots.

Russian media reported only two militant deaths. An Associated Press reporter also saw the body of one militant near Yandare.