"We have information that terrorists are continuing their attempts to access nuclear materials, as well as biological and chemical components," Alexander Bortnikov said at a news conference after a meeting of the heads of security services from the member states of the Commonwealth of Independent States (CIS).

He said the possible use of nuclear components by terrorists in preparing attacks was separately discussed at the meeting.

"We are constantly paying attention to this issue," he said.

He did not specify which terrorist groups he believed were seeking nuclear materials.

The safety of nuclear stockpiles was the focus of the April 12-13 international nuclear security summit in Washington.

Russian President Dmitry Medvedev stressed at the summit the risks of terrorists obtaining nuclear material.

"This is a real threat, and we should work to counter it," Medvedev said.