The US Department of Defence is working out a high energy laser which can become one of the elements in the missile defence system. This has become known to RIA Novosti from the Russian military sources. According to their data, the expenditures on this weapon are not compensated by its effectiveness. In cloudiness or in other unfavourable weather conditions the possibility to hit air or space objects is minimum, pointed out the sources. However, the sources told RIA Novosti, this work "can serve as an impulse for a new stage of the arms drive in the countries which will be forced to react to the raising of the military-technological level of security by the United States." "This step will not stop extremists or potential aggressors; on the contrary, it will impel them to work out and use new destruction technologies," RIA Novosti was told by the military sources who commented on the theme of the missile defence system.