Moscow ? With a pair of powerful blasts on Moscow subway cars that killed at least 38 people Monday, two female suicide bombers shattered Prime Minister Vladimir Putin’s claim to have contained a separatist insurgency in Russia’s southwest and forced the nation’s capital to brace for a terrorist comeback after several years of calm.

The explosions occurred about 45 minutes apart at downtown stations during the morning rush hour. They followed triumphant reports in recent weeks that Russian security forces had killed several top leaders of the Islamist rebel movement, which seeks to establish a fundamentalist state in the North Caucasus region.

The elimination of each militant leader was portrayed as a victory for Putin’s tough approach to suppressing the insurgency, which had not mounted an attack in Moscow in nearly six years. “We have been able to break the spine of terrorism,” Ramzan Kadyrov, the Kremlin’s strongman governor in Chechnya, declared two days ago.

But as crowds of dazed, bloodied passengers emerged from smoke-filled subway stations Monday, and national television showed images of mangled bodies strewn on subway cars and station platforms, officials acknowledged the obvious: The rebels had not been defeated, and they appeared to be making good on threats to stage attacks again not just in their volatile homeland but in the heart of Russia.

“Blood will no longer be limited to our cities and towns. The war is coming to their cities,” the rebel leader, Doku Umarov, warned in a video interview posted on the Web last month. “If Russians think the war only happens on television, somewhere far away in the Caucasus where it can’t reach them, then God willing, we plan to show them that the war will return to their homes.”

There was no immediate claim of responsibility for the deadly bombings, which also injured more than 70 people. But Alexander Bortnikov, director of the Federal Security Service, or FSB, said preliminary evidence indicated the attacks had been committed by “terrorist groups linked to the North Caucasus region.”

The first blast occurred shortly before 8 a.m. as the doors were closing on a packed train at the Lubyanka station, located under the headquarters of the FSB, the main successor to the Soviet-era KGB. The location prompted speculation that the attack was intended as revenge, because the FSB has led the Kremlin’s sometimes brutal efforts to crush the insurgency in Chechnya and the rest of the North Caucasus.

A smaller explosion took place at the Park Kultury station, four stops away on the same line. Officials said evidence at the scenes, including body parts, indicated both bombers were women wearing belts packed with explosives as well as bolts and iron bars that acted as deadly shrapnel.