The death toll of gun battles that erupted between Chechen rebels and security forces in Grozny have risen to 19, including 10 officers, authorities said.
Violence broke out in the capital of the Russian republic in the northern Caucasus last night, as gunmen travelling in three cars entered the city shooting three traffic police officers dead at a checkpoint, the National Anti-Terrorist Committee said.
The militants occupied a 10-story Press House in the city centre and stormed a nearby school. The institute was empty at the time of the attack.
Security forces subsequently launched an attack on the two buildings that resulted in at least another seven officers and nine rebels being killed.
The National Anti-Terrorist Committee said 28 officers were wounded in the fight.
The violence came only hours before President Vladimir Putin was to make his annual state of the nation address.
Dmitry Trenin, the head of the Carnegie Moscow Center, said militants were most likely trying to "embarrass Putin".
In his speech, Putin suggested the gunmen were backed by foreign organisations, adding that he trusted Chechen forces were capable of dealing with them.
The attack marked a major shift in the fragile period of stability in the region, which has been enforced by the brutal rule of Chechnya's Kremlin-appointed leader, Ramzan Kadyrov.
Kadyrov, who was in Moscow for Putin's speech, said the rebels were Islamists linked to Doku Umarov, an infamous Chechen militant leader who died earlier this year.
In an Instagram posting, the ruthless leader said all gunmen at the Press House had been killed and the situation was now under control.
"Not one bandit managed to get out," he wrote.
A man claiming to operate under orders from Chechen Islamist leader Aslan Byutukayev, known to his followers as Emir Khamzat, claimed responsibility for the violence in a video message published by the Kavkaz Center website, a mouthpiece for Islamic militant groups in the region.
The video could not immediately be verified.
Chechnya, a largely Muslim region, fought two separatist wars against Russia in the 1990s and has experienced outbursts of Islamist violence ever since.
However in recent years, Kadyrov's forceful security measures appeared to have largely quelled the Islamist insurgency.
The security success was marred by human rights groups making accusations of kidnap, torture and murder of opponents against Kadyrov.