Authorities have warned that the death toll from the bomb blast could rise, with many people in critical condition [AFP]

Russia's president has vowed tough action against those responsible for a deadly bombing in the North Caucasus, while a rebel leader has urged fighters to carry out more attacks.

Dmitry Medvedev vowed on Friday to destroy the "bandits" behind a suicide attack in Vladikavkaz, the North Ossetian capital, that killed at least 17 people and wounded more than 100 others.

His comments came as Doku Umarov, leader of an armed Chechen separatist movement, urged fighters in an online video to focus on "taking jihad beyond the boundaries of the Caucasus" in order to "batter Russia in its den".

The video, posted on kavkazcenter.com, a Checheb separatist website, was dated September 2010 and cast as a Ramadan message to fighters in the Muslim-majority Tatarstan and Bashkortostan provinces.

No group has yet claimed responsibility for Thursday's attack, in which a car carrying around 40kg of explosives packed with metal bars, bolts and ball bearings detonated in a busy city market. 

Arrests made

Russian police have detained three people with suspected links to the bombing, but an investigation is still underway.

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Neave Barker, Al Jazeera's correspondent in Moscow, said investigators were combing the scene for clues to the attack throughout Friday.

"While there has been no claim of responsibilty, authorities are almost certain the attack was part of the ongoing Islamist insurgency across the North Caucasus," Barker said.

"The response from the Kremlin has been swift and strong. Vladimir Putin, Russia's prime minister, ... has called on Muslims to help the fight against home-grown terrorism.

"The attack is a clear message to Russians that despite counter-insurgency efforts, local authorities and ordinary citizens remain very much at risk."

Death toll 'could rise'

As officials declared a day of mourning in the Russian republic on Friday, residents laid flowers in the blood-stained market, while government buildings flew flags at half-mast.

With many of those injured in a critical state, and identification of body parts still incomplete, there are fears the death toll could rise further.

A three-year-old child is reported to be among those critically injured. His 18-month-old brother had already died in the blast.

North Ossetia is seen as one of the Caucasus' more stable areas, unlike the republics of Chechnya and Dagestan, which see violence between separatists and Russian forces on a regular basis.

However, the republic does suffer from ethnic tensions and has seen a rise in unrest in recent months.

In November 2008, the mayor of the city was killed when an assassin shot him in the chest near his home.

It was also the scene of the 2004 Beslan massacre, in which Chechen separatist fighters took hundreds of hostages at a school - a siege that ended in the deaths of 330 people, around half of them children.

Unlike most other Caucasus provinces, where Muslims make up the majority of the population, North Ossetia is predominantly Orthodox Christian.

The market attack came as Muslims were preparing to celebrate Eid al-Fitr, a holiday marking the end of the holy month of Ramadan.

Source: Al Jazeera and agencies