Interior Ministry sources named the arrested man as Dmitry Pimenov - said to be the leader of the Union of Revolutionary Writers, a group protesting against growing consumerism in Russia.

A leaflet signed by the group was found at the site of the explosion.

Moscow Echo radio, reporting the arrest, said no charges had been brought against Mr Pimenov.

It said police had traced him from a photograph on the group's website, but added that the investigation into the blast was following several leads.

The explosion ripped through an amusement arcade on the bottom floor of the Manezh shopping and restaurant complex.

An adjacent row of fast food restaurants were showered with broken glass and metal shards, injuring dozens of tourists and late-night shoppers.

"Philistines, we don't like your way of life," the note from the Union of Revolutionary Writers said.

"A hamburger not eaten to the end by the dead consumer is a revolutionary hamburger."

Officials said they had not heard of the group before.

Terrorism fears

The explosion has triggered fears of political violence returning to Russia.

Russian media have suggested it might be linked to Islamic militants who are waging war against Russian rule in the Caucasus or to political battles in Moscow itself.

A third suggestion is the possible settling of scores between rival Mafia groups.

There are large numbers of bomb attacks in Russia each year, often involving criminal groups or business rivals seeking to settle turf battles. This was the second major explosion to rock the Russian capital this year.