"Look, we continue to have discussions with the government of Poland on this," Casey said. "(We) very much would like to conclude an agreement and do so in the very near future, but ultimately this is a negotiation, a negotiation among friends and allies."
The matter is of mutual importance to the two countries, Casey told reporters during a Tuesday briefing.
"The prime minister said he believed that the stationing of the interceptors in Poland was something that was in Poland's national interest and the interest of its national defense," the State Department spokesman said.
2014: The Year in Music [PHOTOS]