A U.S. agreement with Poland to send 1,000 extra troops to the country is a defensive measure needed for its security, the U.S. ambassador to Warsaw said on Monday, replying to accusations from neighboring Russia that the move is aggressive.

U.S. President Donald Trump's pledge last week to dispatch the troops to Poland was a step sought by President Andrzej Duda because of past Russian aggression against Poland and to help solidify his country's ties to the West.

Russian Deputy Foreign Minister Sergei Ryabkov was quoted as saying by the Russian state-run RIA news agency last week that Washington's move probably reflected "aggressive" intentions.

Another lawmaker, ex-commander of Russia's special forces Vladimir Shamanov, said he was concerned that the U.S. drones could be capable of carrying nuclear weapons at some point.

In response, U.S. Ambassador Georgette Mosbacher said that "what we're talking about is merely defensive, (making) a country enabled to defend its borders."