MOSCOW - In a stunning return to siege-style violence in the Russian region of Chechnya, well-armed Islamist militants seized an empty school and office building Thursday before an hours-long shootout that pushed the death toll to at least 20, authorities said.

The bloodshed in Grozny - where at least 10 militants and 10 police officers were killed and 28 wounded, said the National Anti-Terrorism Committee - was an unwelcome reminder of the 1990s strife in Chechnya between Russian forces and separatist insurgents.

The region has since experienced relative peace in recent years under the strong-arm governance of Kremlin-allied President Ramzan Kadyrov.

The timing of the attack also suggested an attempt to maximize the blow - coming just hours before Russian President Vladimir Putin delivered an annual state of the nation speech in Moscow. Putin gained much of his initial political credibility as Russia's leader by shutting down the insurgency and from his tough approach to Chechen-linked terrorist attacks elsewhere in Russia.

"These rebels have showed up in Chechnya again," Putin said in the speech to Russia's political elite in a glittering Kremlin hall. "I'm sure the local law enforcement authorities will take proper care of them."

The violence began early Thursday when a group of gunmen in three cars attacked police at a checkpoint, killing three officers, said the National Anti-Terrorism Committee. The militants then moved on to seize a 10-story publishing house in central Grozny and a nearby school. Russian news outlets said that, because of the early hour, no teachers or students were inside.

Authorities surrounded the publishing house, killing at least six insurgents, Kadyrov said on his Instagram account. A fire gutted the building, and the body of at least one civilian was found in the rubble, the Interfax news service reported.

"We destroyed the devils," Kadyrov told reporters in the Kremlin after Putin's address. He said he had personally directed the security response before flying from Grozny to Moscow for the speech.

A person proclaiming links to the Caucasus Emirate claimed responsibility for the attack in a YouTube video, but the claims and the source of the video could not be immediately verified. In the video, which appeared to have been shot on a cellphone at night, the unidentified man said that he and his compatriots were on a suicide mission and that "many mujahideen have entered the city."

Islamist rebels in 2007 declared the separatist Caucasus Emirate, an entity that spans several mostly Muslim republics in Russia's Caucasus region and is an outgrowth of the Chechen struggle for independence in the 1990s.

Many Chechens have gone to fight with the Islamic State, the militant group also known as ISIS or ISIL that has seized territory in Iraq and Syria, but Aliaskhab Kebekov, the leader of the Caucasus Emirate, is not believed to have sworn allegiance to the group.

Secular Chechen separatists fought a war with Russian forces after the 1991 breakup of the Soviet Union. In 1999, an insurgency reinvigorated by Islamist ideals sparked a second grinding conflict. Afterward, the republic was put under direct Moscow control.