President Dmitry Medvedev demanded tough action against militants on Friday after a suicide bombing killed at least 18 people, and an insurgent leader called for more attacks outside Russia's Muslim regions.

The remarks from Medvedev and Chechen rebel leader Doku Umarov, who spoke in a web-posted video, underscored the confrontation between the Kremlin and Islamist insurgents who say they are determined to bring Russia down.

"There should be no ceremony with the bandits: they should be destroyed," Medvedev told Russian and foreign political analysts at a forum in the city of Yaroslavl.

He spoke as mourners in North Ossetia left flowers near police barriers at the gates of a busy market in the provincial capital, Vladikavkaz, where authorities say an attacker set off a powerful bomb packed with bolts and ball bearings on Thursday.

An injured victim died in hospital overnight, a regional Health Ministry official said, bringing the death toll to 18 including the suspected attacker. More than 100 people remained hospitalized, including 11 who were flown to Moscow.

The blast was a new blow to the Kremlin, which is struggling to contain a growing Islamist insurgency in the North Caucasus, a strip of impoverished, ethnically mixed provinces along predominantly Orthodox Christian Russia's southern border.

Insurgent leader Umarov issued a new call for attacks outside the North Caucasus.

Umarov, filmed sitting on the ground in an unspecified location and wearing camouflage, urged militants to focus on "taking jihad beyond the boundaries of the Caucasus" and other Muslim regions in order to "batter Russia in its den."

The video on www.kavkazcenter.com was dated September 2010 and cast as a Ramadan message to militants in the heavily Muslim Tatarstan and Bashkortostan, east of Moscow in central Russia, where there has been very little violence linked to Islam.

Umarov has repeatedly vowed to carry out attacks in Russia's heartland. He claimed responsibility for twin suicide bombings that killed 40 people on Moscow's metro in March, which Russian authorities also blamed on the Caucasus-based militants.

The militants, whose campaign against Russian authorities stems from the post-Soviet wars between federal forces and Chechen separatists, have struck outside Muslim areas several times.

Mostly Orthodox Christian North Ossetia is sandwiched among the predominantly Muslim regions of Chechnya, Ingushetia, Dagestan and Kabardino-Balkaria, which are plagued by daily violence linked to the insurgency.

It is the site of the September 2004 Beslan school siege that led to the deaths of more than 330 people, many of them children. But it had largely escaped the violence that has plagued the nearby Muslim regions in the last two years.

In Vladikavkaz small groups of mourners laid carnations outside the police cordon surrounding the site of the blast.

Flags on government buildings flew at half-mast with black ribbons attached, and entertainment programs were canceled on local television.

The Kremlin has been unable to curb the insurgency in the Caucasus a decade after federal forces drove separatists from power in Chechnya in a war launched by Prime Minister Vladimir Putin.

Rights groups say the poverty, corruption and abusive conduct by government forces in the North Caucasus stokes anger at the authorities and fuels the insurgency.