(CNN) -- Explosions from a grenade-launcher attack and then a car bomb rocked a restaurant in the capital of Russia's republic of Dagestan on Friday, injuring at least five people, the state-run RIA Novosti news agency reported, citing local authorities.
The attack in Makhachkala began with a grenade blast on the second floor, followed by a car bomb that exploded after police arrived, RIA Novosti reported.
A law enforcement source told the news outlet that a dispute between criminal gangs could be a motive.
The explosions came amid years of unrest and an Islamist insurgency in Dagestan and the North Caucasus region. They also came as Russian security forces have tried to address security concerns before next month's Winter Olympics in Sochi, perhaps a 12-hour drive west of Dagestan.
Concerns about security in Russia were heightened after twin bombings on public transit that killed more than 30 people in the southern city of Volgograd at the end of last month.
Just Wednesday, four militants and three Russian security force members died in a shootout in Dagestan, which sits on the other side of the Caucasus range from Sochi.
Russian President Vladimir Putin said Friday that his government is doing "everything possible" to make sure the Olympics will be secure. What it will not do, he insisted, is shudder in face of the threats.
"If we allow weakness and fear to come out, to show our fear, that means we will be helping the terrorists achieve their aims," Putin told several television networks, as reported on the state-run RIA Novosti's website.
The same report claimed an apparent milestone in this effort: Doku Umarov, a purported terrorist leader who had threatened to launch attacks in Sochi, was killed by authorities, according to the Kremlin-installed head of the the Chechnyan republic, Ramzan Kadyrov.
Threats from other people remain.
That includes a fatwa -- or religious ruling in line with Islamic law, as decreed by one or more clerics -- posted earlier this month on a website aligned with Chechen rebels, according to the SITE Intelligence Group, which monitors terror-related websites.
In it, a radical cleric defended the Volgograd attacks and backed suicide bombings leading to the Sochi games. Such violence against "Christian disbelievers" is justified in light of Russia's years-long crackdown on Chechen Muslims, according to the cleric.