Issues related to the cross-border movement of allied forces within Europe have been exposed in NATO exercises, U.S. Secretary of Defense James Mattis said in Brussels on Thursday.

"The issue has been partly solved on the local level at the moment, but a standardized procedure is needed," Mattis said at a press conference at NATO Headquarters.

Mattis told journalists on the second day of the two-day meeting of NATO defense ministers that the Netherlands has made a proposal for solving the issue and the EU has decided to realize the proposed solution.

"If you want to have a NATO that is truly capable of protecting the democracies here, you have got to be able to work together, and one of the most fundamental points of that is at the point of borders, where you speed troops across if they are needed somewhere else in the alliance," he explained.

The defense ministers on Wednesday agreed on the key features of the new management structure, which among other things include the creation of the Allied Command Structure for the protection of sea lines of communication betwen North America and Europe as well as improving the movement of troops and equipment within Europe.

Minister of Defence Jüri Luik on Wednesday said that the movement of troops across state borders in Europe is very slow due to bureaucratic obstacles, adding that NATO is working toward streamlining the process.