Russian troops killed some 50 rebels in a recent operation in Russia's breakaway republic of Chechnya, the Interfax news agency reported Sunday, quoting military officials.

Ilya Shabalkin, spokesman for the Russian forces in North Caucasus, told Interfax the operation was conducted on Saturday based on intelligence, suggesting the rebels were planning a large-scale show of military strength for Saturday.

"Russian forces possessed intelligence, revealed rebel camps and launched preemptive blows at them," Shabalkin was quoted as saying.

"The rebels managed to remove many of those killed from the scenes of clashes. But 18 bodies remained at the scene of the fighting and 12 rebels have been detained," he said.

In the clashes, which occurred in Chechen capital of Grozny and in its suburbs, 12 Russian servicemen were killed while 16 civilians were injured, said Shabalkin.

On Saturday evening, Shabalkin told Interfax rebels had attacked a police station in Grozny earlier that day, killing several servicemen and wounding a few others.

On Sunday morning, Russian President Vladimir Putin paid an unannounced visit to Chechnya and laid a wreath at the grave of slain former Chechen President Akhmad Kadyrov, according to Russian media.

Chechnya is preparing for early presidential elections next Sunday to elect a president to succeed Kadyrov.

Chechnya, a war-torn republic in Russia's Northern Caucasus, won a status of de-facto independence in 1996 after the pullout of Russian troops.

Russian troops re-entered the lawless region in September 1999 following attacks by Chechnya-based terrorists in a neighboring region and a series of deadly bombings blamed on the rebels.