ROME — In a careful speech in Rome on Friday, NATO head Jens Stoltenberg welcomed European plans for a tighter defense capability, but warned the continent against creating an "alternative" to NATO.

"Stronger European defense will be good for the European Union, it will be good for Europe and will be good for NATO," he said. But he added: "We must make sure to avoid duplication with NATO structures and that what Europe does is complementary to NATO."

EU members Italy, France and Germany have revived plans for EU Battle Groups and a unified military command structure since the UK voted to leave the EU this year, after years of opposing such plans.

In a concrete example of EU-NATO cooperation, Stoltenberg told Italian newspaper La Stampa on Friday that NATO would increase cooperation with Operation Sophia, the EU naval operation in the Mediterranean tackling people trafficking. NATO would cooperate with the EU on the training of Libyan coast guards to help stem the flow of migrants sailing from Libya, he said.

Speaking in Rome on Thursday, NATO’s military committee chairman, General Petr Pavel echoed Stoltenberg’s cautious welcome of an EU military capability.

"We still have a number of deficiencies in a our defense capabilities and we see an increasing European pillar of defense is a crucial pillar for NATO," said the Czech general.

"We see these initiatives as complementary and mutually reinforcing," he said. "Obviously we will be watching the process very carefully and trying to assist as much as possible in using all existing capabilities we have for more effectiveness to avoid duplication and competition, because such competition would be very unhealthy."

Asked about where potential duplication could arise, he cited command structures.

"NATO has developed over the years a command structure at all levels, from tactical up to strategic and it is well proven in crises and operations," he said.

"The EU has expressed a will to develop their own autonomous command structure and in that sense I believe though there is a need to have a permanent command element, specially to plan EU operations, any effort to mirror the structure of NATO would be a competition for resources because two thirds of the nations in NATO and the EU are the same."

If NATO members were already reluctant to spend on NATO command structures, why should they also spend on EU structures, he asked.

"The EU already has elements of a command structure. It has a military committee, an international military staff, a civil-military planning directorate, a situational centre," he said.

"I believe if these elements are brought together to create a permanent structure we are on the right track. If they try to build something from scratch it would need funding and human resources and we would get into trouble because these resources are scarce."

In operations, NATO and the EU needed to look for synergies, he said.

"Missions will be increasingly ‘Pol-Mil’, not just military so we will have to focus on both elements, security and development at the same time," he said.

"NATO does not have many tools to address development while the EU has a lot of these tools. If we focus on identifying problems, then identifying the tools necessary to address the problems, then we can decide which institution can address which problem, and if we can think about how to coordinate a joint effort, then we will be much better off than trying to suggest who will be more autonomous and who will be more in control of the process."

Addressing the growing threat from Russian aggression, Stoltenberg said on Friday that NATO needed "continue pursuing our policy of strong defence combined with political dialogue."

Italian Foreign Minister Paolo Gentiloni said on Friday that Italy would send 140 troops to join other NATO troops manning the borders of the Baltic states with Russia.

"We do not see Russia as an enemy, but we have to see it at least as a strategic competitor," said General Pavel.

Turning to Turkey’s new friendship with Moscow, Pavel said there was a potential upside.

"I see the relationship between Turkey and Russia not as a threat but as a natural consequence of Turkey being exposed to so many challenges," he said. "Communication between Turkey and Russia may help ease the tensions between NATO and Russia. If we take a healthy approach to this issue, we can use it as an advantage and not a disadvantage."