Russian President Vladimir Putin says Moscow has no choice but to retaliate over the U.S. missile shield in Europe.
Speaking during a visit to Athens on May 27, Putin also warned that the presence of elements of the shield in Romania and Poland would put people living there in danger.
"If yesterday in those areas of Romania people simply did not know what it means to be in the cross-hairs, then today we will be forced to carry out certain measures to ensure our security," Putin said. "It will be the same case with Poland."
Putin, who did not elaborate on how Russia would retaliate to the missile shield, also insisted that Russia was not taking the first step, only responding to moves by Washington.
Moscow has long said the establishment of a U.S. missile defense system in Eastern Europe poses a threat to Russia's security.
Washington has repeatedly said the systems will protect NATO members from short- and medium-range missiles, particularly from rogue states in the Middle East.
Poland on May 13 broke ground on the northern section of the U.S. missile defenSe shield that was launched in Romania a day earlier. The system is due to become fully operational by 2018.