The death toll from the worst militant strike for months in Russia's conflict-torn Caucasus rose to at least 17 Friday as the troubled region of North Ossetia observed a day of mourning.

A suicide car bomber wounded more than 100 people Thursday at a busy central market in the city of Vladikavkaz in the mainly Christian Caucasus region of North Ossetia.

More people died of their injuries overnight, raising the death toll to 17, said regional health minister Vladimir Selivanov, while Maria Gatsoyeva, a spokeswoman for regional investigators, said there were 18 dead.

An official involved in the identification of the bodies told AFP the death toll could rise even further when authorities complete the identification of body parts.

"We have really small fragments at our disposal and we cannot understand to how many people they belong," the official told AFP on condition of anonymity, estimating the toll could rise to 25.

The Ukrainian foreign ministry said a Ukrainian woman was among the dead, the Interfax news agency reported.

Doctors scrambled to save the wounded but officials warned the death toll might go up as some of them, including a three-year old, were in a critical condition.

The child's 18-month old brother died of his injuries on Thursday.

The shrapnel-littered market, which has seen several attacks in the past decade, remained cordoned off as investigators continued their probe and grieving locals brought carnations to the scene of the tragedy.

 "How should we live and what should we do with our children to protect them?" said Bella Tavasiyeva, one of the mourners.

Locals worked through the night to re-glaze windows in a nearby school shattered by the blast and while classes were not officially cancelled many schoolchildren stayed at home.

President Dmitry Medvedev, speaking to international experts in the Volga city of Yaroslavl, asked them to join him in a moment of silence in honour of those killed and reiterated his vow that the organisers of the bombing would be caught.

"Terrorists implicated in this crime will be eliminated," he said in televised remarks.

Speaking earlier in the day Medvedev said "there should be no ceremony with the bandits" and local authorities "should not sit in their palaces" but be in touch with ordinary people, including those who do not agree with their policies, the ITAR-TASS news agency reported.

Officials declared Friday a day of mourning in North Ossetia as flags at government buildings flew at half mast and television entertainment programmes were cancelled.

Located to the north of the Georgian breakaway region of South Ossetia, North Ossetia is the only majority-Christian region in Russia's largely Muslim North Caucasus.

Authorities said the blast was triggered by a suicide bomber who drove up to a busy market in an explosives-packed car and whose headless body was later discovered.

The suicide attack was the most serious in Russia since double bombings carried out by two female suicide bombers on the Moscow metro on March 29 killed 40 and wounded more than 100. 

 It was the deadliest attack in the Caucasus since a truck bombing outside the police headquarters in Ingushetia in August 2009 killed 24.

The attack came as Russia's Muslim regions were preparing to celebrate Eid al-Fitr, a Muslim holiday that marks the end of the holy fasting month of Ramadan.

The head of the FSB security service, Alexander Bortnikov, said Thursday evening that three people had been detained on suspicion of involvement in the attack.