All of NATO's coordination centers in Bulgaria, Romania, Poland, and the Baltics are due to be operational by the end of this year, the Alliance's Secretary General has said.

On the first day of talks held in Brussels by Defense Ministers of NATO members, Stoltenberg has explained each of the centers will have 40 employees and will work in line with arrangements agreed during the major changes of the Eastern Europe strategy last year.

Earlier this week Romanian MPs approved the construction of coordination centers on its territory.

This comes against the backdrop of a hastily prepared plan to station heavy weapons in the six states which stirred up some controversy in Bulgaria.

Speaking to counterparts, US Defense Secretary Ashton Carter confirmed that Washington was planning the deployment to bolster the Alliance's eastern flank.

Bulgarian authorities had confirmed a few hours earlier they had consented to receiving heavy equipment, but added the permission as only about temporary deployment aimed at carrying out joint military drills.

"We do not seek confrontation; we do not want a new arms race... But we have to keep our nations safe. And we have to adapt when the world is changing," Fox News quotes Stoltenberg as saying.

The total deployment includes some 90 Abrams battle tanks, 140 Bradley armored vehicles, and 20 self-propelled howitzers. These units, however, will be scattered across the six NATO states, and not concentrated in a single area.

Measures such as doubling NATO's rapid response force to 40 000 - up from 13 000 - were also approved on the first day of the meeting. An agreement was reached to make it easier for NATO generals and civilian officials to mobilize the forces, Stoltenberg informed.

As tensions between Moscow and the West are still mounting over the situation in Ukraine, Russia has been upgrading its own capabilities and has moved to add 40 nuclear ballistic missiles to its arsenal this year.