Ukraine and the United States strengthened their military collaboration on Thursday with a five-year agreement, including to supply military equipment and train soldiers.
"This is the first time in history that we have signed such a document for such a long period," Ukrainian Defence Minister Stepan Poltorak told reporters in London, where he inked the deal with his US counterpart Ash Carter.
In addition, retired US General John Abizaid will serve as an adviser to Ukraine's Defence Ministry. Since 2014, the US has given Ukraine military supplies worth the equivalent of more than 600 million dollars.
Britain also announced that it would help train Ukrainian military forces.
Tensions between Ukraine and Russia have escalated in recent weeks, with both countries putting troops on full combat alert.
The Ukrainian military has been fighting sporadic battles against Russian-backed rebels in Ukraine's two eastern-most regions for the past two years.