A Ukrainian soldier in the town of Avdiyivka in the Donetsk region in November
The U.S. Defense Department has announced a resumption of millions of dollars in military assistance to Ukraine after it was frozen last year, putting it at the heart of the impeachment of President Donald Trump.

The Pentagon said $250 million will be released to assist with "training, equipment, and advisory efforts to strengthen Ukraine's capacity to more effectively defend itself against Russian aggression."

A Pentagon statement says the aid reaffirms the long-standing defense relationship between the United States and Ukraine, adding that the country is "a critical partner on the front line of strategic competition with Russia."

The support will complement NATO security assistance to Kyiv and comes after the United States certified the Ukraine government had implemented required reforms in the military, the Pentagon statement said.

Over the past year, Ukraine has taken "considerable steps" to strengthen civilian control of the military, reform management and command structures, and reduce corruption, it said.

The United States and other Western countries have expanded support of Ukraine's military since Moscow seized control of the Crimean Peninsula in March 2014 after sending in troops and staging a referendum dismissed as illegal by at least 100 countries. Moscow is also backing separatists in a war in eastern Ukraine that has killed more than 13,000 people since April 2014.

The Pentagon statement says the United States continues to urge all allies and partners to enhance their support for Ukraine's security and defense.

Last year, Trump froze hundreds of millions of dollars in military aid to the country while he sought help from the government to investigate former U.S. Vice President Joe Biden, his Democratic challenger in the November presidential election.

Democrats said Trump's request amounted to a quid pro quo for military aid and launched an impeachment inquiry for abuse of power and obstruction of Congress.

Trump was acquitted by the Senate early this year.