Russian president Vladimir Putin said that he was concerned about the positioning of US missiles in Bulgaria and Romania.

In April 2006 Bulgaria and the US signed an agreement for defence co-operation, according to which US troops would use military bases in Bulgaria.

If US continued building up its anti-missile shield, Moscow could get ready to react, Putin told journalists from the G-8 countries.

US nuclear potential appeared on the European continent for the first in its history, Putin said as quoted by Bulgarian National Radio. ''This changes the whole configuration of international security'', Putin said.

According to the US, anti-missile shield was needed to counter eventual threat from Iran.

The anti-missile defence was 'ridiculous' because it aimed at defending from something which did not exist, Putin said.