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Debris from a car bomb attack is pictured in Kizlyar, Russia. Suicide bombers killed at least 12 people in the North Caucasus on Wednesday. ((S. Dal/Reuters))

Russian President Dmitry Medvedev called for tougher anti-terrorism measures Thursday after making a surprise visit to the southern province of Dagestan, where suicide bombers killed 12 people Wednesday.

Medvedev told local officials "the measures to fight terrorism should be expanded, they should be more effective, more harsh, more cruel."

Russia was hit by two major terrorist attacks this week. On Monday, suicide bombers struck two metro stations during the morning rush-hour commute, killing 39 people.

Wednesday's deadly attacks happened in the town of Kizlyar, near Dagestan's border with Chechnya, where Russian forces have struggled to contain a separatist insurgency. Nine of the 12 people killed in the attacks were police officers, local officials said.

The violence in the troubled region continued Thursday, when two suspected militants died in an explosion in Dagestan. Police said the men may have been transporting a makeshift bomb.

No group has claimed responsibility for Wednesday's attacks, but Doku Umarov, leader of a Chechen militant group, claimed responsibility for Monday's metro attacks. Umarov said the twin suicide bombings were retaliation for the killing of civilians by Russian security forces.

Alexander Bortnikov, the director of the Federal Security Service, joined Medvedev in Dagestan on Thursday. He said security officials had identified the organizers of the Moscow attack as "bandits" from the North Caucasus region and said some of them had been detained, but he didn't provide specific details.

Funerals held for subway victims

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Relatives and friends grieve over the body of Anna Permyakova, a victim of the subway blasts, during a funeral ceremony in Moscow. ((Alexander Natruski/Reuters))

More than a dozen funerals were held in Moscow Thursday for victims of Monday's suicide bombings, with several more scheduled for Friday.

At the Khovanskoye cemetery, family, friends and colleagues of Anna Permyakova, a 34-year-old nurse, wept as they placed flowers on her open casket. Permyakova had worked in a rehabilitation centre and many of her former patients attended the funeral in wheelchairs.

Monday's attacks happened inside the Lubyanka and Park Kultury metro stations. Two female suicide bombers detonated explosives as the trains pulled into the busy stations, police said.

On Wednesday, several thousand people congregated at Lubyanka station for a memorial service honouring the victims of the subway attacks.

More than 70 people are still recovering in hospital, with at least five people in critical condition, officials said.

With files from The Associated Press