The Kremlin's military operation, which formally ended in the volatile republic last week, was restarted in the Shatoi, Vedeno and Shali districts at midnight on April 23 as after "activity was observed among illegal armed groups."
Earlier this week, gunmen killed three Russian soldiers in the Chechen village of Bamut, near the border with Ingushetia. Despite the formal end of the operation, several thousand Russian troops had remained in the province to counter militant activity in mountains districts.
Federal troops and police have arrested three militants and five accomplices, and found 10 terrorist hideouts, and six arms caches in southern Chechnya.
The spokesman said three powerful explosive devices, believed to be targeting Chechen government escort vehicles, had been discovered in the Vedeno district.
Russian federal troops launched the counter-terrorism operation in Chechnya in the fall of 1999 after a group of militants led by Shamil Basayev and Arab mercenary Khattab invaded neighboring Daghestan. Moscow conducted a separate campaign in Chechnya in 1994-1996.
Under President Ramzan Kadyrov, the republic has seen a decline in militant activity, although attacks on federal forces remain common. The 32-year-old Chechen leader has been accused by his critics of involvement in human rights abuses, a charge that he denies.
On Tuesday, Kadyrov played down reports of impending terrorist attacks, saying the security situation in the south Russian republic remained stable and under control.
Russian media had quoted the Interior Ministry as saying militant forces were gathering strength in mountainous areas and preparing a series of terrorist attacks in the capital, Grozny.