Alexander Bortnikov, the chief of the FSB, the main successor to the Soviet-era KGB, gave no further details about the attempts or which groups had sought the materials.
"We have information which indicates that terrorists are continuing to attempt to get access to nuclear materials (and) biological and chemical components," he was quoted as saying by Interfax.
Meanwhile, several FSB members were killed while attempting to detain a rebel group linked to the Moscow metro bombings, Bortnikov said.
"Literally yesterday (Tuesday) we carried out a special operation in Dagestan. Unfortunately as a result of the special operation, FSB troops were killed, some were wounded," he said.
"We were working against the band that is linked to the explosions in the Moscow metro," said Bortnikov, according to the RIA Novosti news agency. He did not give a precise figure for the number killed.
Two suicide bombings in the Moscow metro on March 29 killed 40 and wounded more than 100.
