MOSCOW -- Russia's counter-terrorism agency has arrested two brothers suspected of assisting the suicide bombers who struck the southern city of Volgograd in late December.

The bombings of a train station and trolley bus in Volgograd, which killed 34 people and wounded many more, heightened security fears ahead of the Winter Olympics in Sochi.

The National Anti-Terrorism Committee said Thursday in a statement that Magomednabi and Tagir Batirov were detained in Dagestan, a predominantly Muslim republic that has become the centre of an Islamic insurgency. They are suspected of helping the suicide bombers travel to Volgograd, about 650 kilometres to the north.

The agency also released the names of the suspected bombers -- Asker Samedov and Suleiman Magomedov -- saying they were members of a terrorist group based in Dagestan.