DUSHANBE - Russian investigators were in Tajikistan on Tuesday, questioning the families of four men charged with carrying out a deadly attack on a concert hall near Moscow, three Tajik security sources told Reuters.

The sources, who were not authorised to comment publicly, said Tajik security officials had brought the families to the capital of Dushanbe from the towns of Vakhdat and Gissar, and from the Rudaki district.

Tajik President Emomali Rakhmon was personally overseeing the investigation on the Tajik side, the sources said.

On Monday, making his first public comment on the attack, Rakhmon called it a "shameful and terrible event" and urged Tajiks to protect their children from harmful influences.

Four men of Tajik origin have been remanded in custody on terrorism charges, on suspicion of carrying out the attack. Three others, also of Tajik origin, were remanded on suspicion of complicity.

Islamic State has said it was responsible for the attack and has released video footage that it says shows the massacre.

  - Reuters