US Vice President Joe Biden: "Poland is one of our closest allies"
Polish Prime Minister Donald Tusk has declared his country ready to take part in a revised US missile defence plan.
Mr Tusk told visiting US Vice-President Joe Biden that Poland was "ready to participate".
Poland will now host a small US base equipped with short-range missiles. It replaces a much bigger system favoured by former President George W Bush.
Mr Biden insisted the new system was better than the old version and would mean "better security for Poland".
President Barack Obama's decision to scrap Bush-era plans to build a defence system in Poland and the Czech Republic caused some alarm in those countries.
The White House's decision to reset its relations with Moscow, which had vehemently opposed the plan, led some to wonder whether Washington was still listening to Central and Eastern Europe's concerns about Russia, says the BBC's Adam Easton in Poland.
Mr Biden's visit is meant to reassure those countries that America's commitment is unwavering, our correspondent says.
He will travel from Poland on to Romania and the Czech Republic.
The US has reconfigured its plans to protect against "rogue" states
After meeting the Polish prime minister Mr Biden said: "We appreciate Poland has stepped up and agreed to host an element of the previous missile defence plan, and we now appreciate that Poland's government agrees with us that there is now a better way... with new technology and new information, to defend against emerging ballistic missile threats.
"It's going to meet it with proven technology that will cover more of Europe, including Poland, and will do it more efficiently than the previous system could have or did.
"Simply put, our missile plan is better security for Nato and is better security for Poland."
The new missile system could be installed by 2015.
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