The file photo shows that the air defense missile system Patriot from U.S. is seen in Tobruq Legacy 2017 held in Siauliai, Lithuania, on July 11, 2017. (Xinhua/Alfredas Pliadis)

WASHINGTON, Nov. 17 (Xinhua) -- The U.S. State Department has approved a possible sale of the Patriot Anti-Missile System to Poland at an estimated cost of 10.5 billion U.S. dollars, said the Pentagon on Friday.

The proposed sale will increase the Polish military's defensive capabilities without altering the basic military balance in the region, said the Pentagon in a statement.

The deal will also give Poland "greater flexibility to conduct air and missile defense operations" with the United States and other NATO members, said a U.S. State Department official.

Currently, the Netherlands, Germany, Spain and Greece are among the NATO members who possess the Patriot system, according to the official who spoke on the condition of anonymity.

Russian President Vladimir Putin has called the missile defense systems in Eastern Europe a "great danger," saying Russia will enhance its own missile strike capability in response.

Putin said earlier the launch areas in Romania and Poland may be used for deployment of short and medium range missiles, which not only presented additional threat to Russia but also could be the prologue of breaching Intermediate-Range Nuclear Forces (INF) Treaty.

Warning of a new arms race, Putin vowed that Moscow would not be dragged in but would take responsive measures to any national security threat.

The contract still requires approval from the U.S. Congress.