ROSTOV-ON-DON - Rescue crews in the Chechen capital Grozny on Friday picked through the rubble of a police precinct building destroyed by an explosion, as officials said the death toll from the blast had risen to at least 24.

The Thursday night explosion blasted a huge hole in the police building in the Zavodskoi region of Grozny, killing at least 24 people and leaving another 18 injured, said Ruslan Avtayev, Chechnya's emergency situations minister. Two Chechen policemen were found alive in the rubble Friday morning and rescue operations continue, he said.

Avtayev said the explosion, which occurred on the second floor of the four-story building, was aimed at top Chechen police officials who were holding a meeting on the third floor on Thursday night.

Investigators at the scene found fragments of an explosive device in the rubble, the Interfax news agency quoted Chechnya's prosecutor Nikolai Kostyuchenko as saying. The discovery appeared to rule out a gas leak as a cause of the explosion - which officials earlier said they could not rule out.

Kostyuchenko said the device, which had explosive power equivalent to 30 kilograms (66 pounds) of TNT, may have been planted by a "former or current police officer" who had access to the precinct building, the ITAR-Tass news agency reported.

Suleiman Vagapov, an inspector with the office of federal envoy for Chechnya, said the explosion was likely staged by a "mole," but added that police chief from the town of Kurchaloi detained recently on suspicion of cooperating with rebels had no relation to the bombing.

The police chief was taken into custody after two officers under his command were detained and gave evidence against him, ITAR-Tass reported, quoting law enforcement sources in Chechnya. The police chief is believed to have led a group of 10 people, including police officers, who were involved in terrorist activity.

In the course of their investigation of this group, authorities found a cache of weapons, explosives and explosive devices, ITAR-Tass said.

Chechnya's fledgling police force has been at the center of a fierce debate between the Moscow-backed administration in Grozny and Russian federal forces.

Administration officials say that the republic's police force - composed mostly of ethnic Chechens - is capable of providing the necessary security in Chechnya, and that Russian federal forces should cede authority to them.

At the same time, Chechen rebels consider the Chechen police as traitors and have increased their attacks on them.

Officials in Chechnya are eager to show that life is returning to normal in Grozny, but after three years the republic remains mired in the three-year war - the second in a decade. At least eight Russian servicemen have been killed in a series of rebel shellings and mine explosions since Thursday, said an official with the pro-Moscow Chechen administration who asked not be named.

Russian forces left Chechnya in 1996 suffering a defeat in the first, two-year war but returned in 1999 after rebels raided a neighboring region and after Russian authorities blamed the rebels for a series of apartment bombings in Russia that killed more than 300 people.