WASHINGTON, September 18 (RIA Novosti) - U.S. Secretary of State Hillary Clinton said during a speech at the Brookings Institute on Friday that Poland and the Czech Republic would remain the key candidates to host a missile defense shield.

During her speech, Clinton dismissed critics who believe the move by U.S. President Barack Obama to scrap missile defense systems in both countries will leave Europe vulnerable to missile attacks.

She said the U.S. would continue to work closely with Poland and the Czech Republic on a missile defense system.

According to the Obama administration's new plan, land-based missile defense shields will not be implemented before 2015. Sea-based defense shields will be operating in the Mediterranean Sea up to 2015.

Obama announced on Thursday that Washington would not deploy missile defense elements in the Czech Republic and Poland, due to a re-assessment of the threat from Iran.

Clinton said the U.S. administration is looking into a more cost effective variant that is more technologically up-to-date and efficient.

The Bush administration sought to deploy a radar station in the Czech Republic and interceptor missiles in Poland as defense against potential strikes from Iran. Russia consistently opposed the plans as a threat to its security and the strategic balance of forces in Europe.

In response to the Bush administration's plans, President Dmitry Medvedev said last November that Russia would deploy Iskander-M missiles in Kaliningrad, which borders NATO members Poland and Lithuania, if the shield was put into operation.