Thousands of troops poured into a southern Russian city Tuesday 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 (search) 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 (search) 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 (search), 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.

Interior Minister Rashid Nurgaliyev told Putin that 15 officers from the Ingush Interior Ministry's central building defended the structure for nearly six hours in a bid to keep rebels from entering the jail cells and freeing captives, the Interfax news agency reported.

Authorities sent in reinforcements shortly after dawn Tuesday, 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 (search).

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.

At least one group of rebels was caught by police as they retreated through Galashki, near the Chechen border, and a firefight was under way late Tuesday, said Yakhya Khadziyev, spokesman for Ingushetia's Interior Ministry.

In Makhachkala, the capital of Dagestan that borders Chechnya to the north and east, three militants were killed by Russian special forces after an hours-long firefight, regional authorities reported.

Maj. Gen. Ilya Shabalkin, spokesman for the Russian forces in Chechnya, blamed Chechen rebels for planning the attacks, but said the raids were carried out by fighters recruited from both Chechnya and Ingushetia.

"The attacks were clearly saber rattling, aimed to demonstrate the rebels' effectiveness to attract funding from foreign terrorist networks," he said, according to the Interfax-Military News Agency.

Earlier, officials noted how some of the fighters shouted "Allahu akhbar" — a frequent rallying cry of Chechen rebels as their insurgency increasingly comes under the influence of radical Islam.

Khadziyev said the death toll was at least 48, including at least 18 police officers and 28 civilians.

Vladimir Yakovlev, Putin's envoy in southern Russia, told Interfax that 47 police were killed and there were a number of civilian deaths, but he said the exact number was still unknown.

Russian television broadcast image of smoke-charred and burning buildings and burned-out vehicles.

Chechnya's Interior Minister Alu Alkhanov told ITAR-Tass that he believed Shamil Basayev, a Chechen rebel commander who has been blamed for some of the most audacious attacks, was behind the foray. The Kremlin is backing Alkhanov in Chechnya's upcoming presidential elections.

Chechnya's separatist President Aslan Maskhadov warned recently that insurgents were preparing to undertake new offensives.

"We are planning to change tactics. Before, we concentrated our efforts on acts of sabotage, but soon we are planning to start active military actions," Maskhadov was quoted as saying in an interview excerpted on Radio Liberty.

Russia's NTV television showed footage of an encounter with some of the presumed attackers, wearing masks and speaking accented Russian, at a border crossing with North Ossetia.

One of the attackers, carrying an automatic weapon, identified the group as "the Martyr's Brigade," according to NTV correspondent Maxim Berezin. The man added, "We have shot everyone here. Go and announce that."

Acting Ingush Interior Minister Abukar Kostoyev, the health minister and a deputy interior minister were killed in the fighting, officials said. ITAR-Tass said Nazran city prosecutor Mukharbek Buzurtanov and Nazran district prosecutor Bilan Oziyev were also killed.

Russian forces withdrew from Chechnya in 1996 after a devastating 20-month war against separatist that left the region with de facto independence. They returned in September 1999, after rebels made incursions into a neighboring region and after deadly apartment-building bombings in Moscow and other cities were blamed on the militants.

Although Chechnya is a largely Muslim region in overwhelmingly Christian Russia, the first of Chechnya's two wars was an essentially secular conflict. However, after Russian troops pulled out when Chechen rebels fought them to a standstill, the separatists increasingly took on a specifically Islamic mantle.