The United States will assist Ukraine's defense sector, U.S. Secretary of Defense James Mattis said, adding that full implementation of NATO standards was expected of Ukraine.

The United States remains committed to assisting Ukraine's defense and supports the Ukrainian defense and security sector reform consistent with international standards, which raises the Ukrainian army's efficiency, Mattis told reporters in Kyiv on Thursday after negotiations with Ukrainian President Petro Poroshenko.

The United States is expecting full implementation of NATO standards, he also said.