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

Russian police have detained three people with suspected links to a suicide bombing in Russia's North Ossetia that killed at least 17 people and left more than 100 injured.

The head of the country's FSB security service, Alexander Bortnikov, said those held were suspected accomplices of the bomber, who detonated an explosive device outside a busy marketplace in Vladikavkav, the province's capital, on Thursday.

"Three have been detained on suspicion of carrying out this terrorist act. At the moment I can only give this information," he was quoted as saying by Russian news agencies.

Nearly 140 people were wounded in the bombing and officials warned the death toll would likely rise as many of the injured were in critical condition.

One person died overnight, bringing the death toll on Friday to 17, although some reports suggested the figure had risen to 18.

Day of mourning

Residents of the city laid flowers in the bloodstained market on Friday, as officials declared a day of mourning in the republic, with government buildings flying flags at half-mast.

Russian authorities began an investigation into the bombing after Dmitry Medvedev, the president, vowed to capture the "bastards" who organised the attack.

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"We will do everything to capture these monsters ... these bastards, who carried out a terrorist act on ordinary people," he was quoted by the RIA Novosti news agency on Thursday.

No group has yet claimed responsibility for the bombing - the deadliest attack since twin suicide bombings on Moscow metro network in March killed 40 people and wounded over 100.

Vladikavkaz is the capital of the Russian republic of North Ossetia, which lies in the restive North Caucasus region.

Meanwhile Barack Obama, the US president, condemned the "terrorist bombing" and offered his condolences to the victims.

"Our hearts go out to the people of North Ossetia, who have already suffered so much from horrific acts of terrorism. We offer our deepest condolences, and stand with the people of Russia in this time of tragedy," he said in a statement.

"This bombing further underscores the resolve of the United States and Russia to work together in combating terrorism and protecting our people."

'Stable' province

The bomb was reported to weigh up to 40kg of TNT equivalent, and stuffed with metal bars, bolts and ball bearings.

It was detonated at the entrance to the city's market where buyers and traders were operating, just before lunchtime.

The region suffers from ethnic tensions and has seen a wave of unrest in recent months [EPA]

Vladikavkaz's market and its surrounding blocks has been the target of several bomb attacks over the past decade or so, in which scores of people have died.

Neave Barker, Al Jazeera's correspondent in Moscow, said the attack could have been a "message" from separatist fighters that "the authorities and the people of the North Caucasus remain as vulnerable as they were six years ago when the Beslan siege took place, despite an increase in counter-insurgency operations".

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