The aid will fund additional training, equipment and advisory efforts to build the defensive capacity of Ukraine's forces, the Pentagon said in a statement.
"This reaffirms the long-standing defense relationship between the United States and Ukraine," the statement noted, adding that U.S. security assistance to Ukraine totalled more than 1 billion dollars since 2014.
It will be determined later when the equipment will be delivered.
The statement came after the White House on Friday rejected a proposal from Russia to hold a referendum in eastern Ukraine on the fate of the region.
"To organize a so-called referendum in a part of Ukraine which is not under government control would have no legitimacy," Garrett Marquis, a spokesman for the White House National Security Council, said Friday.
U.S. media reported Thursday that Russian President Vladimir Putin raised the possibility of a referendum in Ukraine during his meeting with U.S. President Donald Trump on Monday in Finland.
Russia's Ambassador to the United States Anatoly Antonov confirmed Friday that Putin had raised the topic with Trump and made "concrete proposals" on how to handle the conflict.
The conflict in eastern Ukraine started in 2014 between Ukrainian government forces and armed groups which declared independence from Kiev. Ukraine has long accused Russia of aiding the insurgents while Moscow has repeatedly dismissed Kiev's claims.