Moscow and Washington are to cooperate in bolstering the security of nuclear sites against terror attacks, the head of Russia's federal atomic agency said Tuesday.

"Protection technology has to be constantly perfected because of the appearance of new threats," Alexander Rumyantsev said at a press conference.

Russian and US nuclear and defence specialists, as well as diplomats from both sides, have worked for three months to devise measures aimed at strengthening checks on radioactive material and sensitive technology, Rumyantsev said.

The cooperation plan has been sent to US President George W. Bush and Russian President Vladimir Putin, who first announced the idea at their February summit in the Slovak capital Bratislava.

At the press conference, Rumyantsev also raised the possibility of joint US-Russian rapid reaction units to ensure nuclear security in the two former Cold War nuclear foes.