Moscow has held an official day of mourning for the 39 people killed in Monday's twin suicide bombings on the city's Metro.
Russian Prime Minister Vladimir Putin says catching the organisers of the attacks should be a "matter of honour" for investigators.
Security has been stepped up amid fears of fresh attacks.
Officials have blamed the bombings on militants from the North Caucasus.
Rupert Wingfield-Hayes reports.
BBC NEWS CHANNEL
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