NATO chief Jens Stoltenberg said Wednesday that European allies had "much work" ahead to share the defence burden with Washington and also warned the EU to ensure its new defence pact avoids duplicating alliance work.
Despite the differences, Stoltenberg said US Defense Secretary James Mattis and his fellow NATO ministers agreed to modernise its command structure in the face of a more assertive Russia and perceived threats from the Middle East.
"We had a productive and forward-looking discussion on burden-sharing," Stoltenberg told a press conference in Brussels after the first of two days of talks. "We all agreed we have made great progress but there is still much work to be done."
Since he took office more than a year ago, US President Donald Trump has warned NATO allies to meet a goal they set in 2014 of raising defence spending to two percent of GDP over a decade.
Trump's administration has also asked the other 28 NATO member states, mainly European but also Canada, to increase their military capabilities and contribute more to war games.
Stoltenberg said the allies must boost "cash, capabilities and contributions" all together, adding: "It's not either one or the other."
A NATO official told reporters on condition of anonymity the allies all "agreed to focus on the three c's" and "did not push back" when asked to meet their targets, unlike what they had done in the past.
But the official said Mattis told the defence ministers over lunch that their governments will be "watched more closely in the runup" to the July summit in Brussels which Trump is expected to attend.
Stoltenberg said eight NATO members are meeting the two percent target, adding a total 15 of them are expected to do so by 2024 as the others fall short.
The ministers agreed to modernise the command structure with plans to set up an Atlantic command to protect the maritime routes between Europe and North America.
They also decided to establish a new support command to improve the movement of troops in Europe and boost troop rapid response while creating a new operations centre to defend against cyber attacks in Mons, Belgium.
Stoltenberg said the alliance will decide in June where to locate the new commands and how many staff they will have.
The United States has offered to host the Atlantic command and Germany the logistics command, he added.
The NATO ministers later headed to a working dinner with EU diplomatic chief Federica Mogherini, which has taken on greater significance after senior US officials voiced fears about the impact the bloc's new landmark defence pact could have on the balance of power in NATO.
The EU's so-called permanent structured cooperation on defence agreement, known as PESCO, has projects in view already to develop new military equipment and improve cooperation and decision-making.
But on Sunday a senior official working with Mattis said Washington had concerns that some of the proposed initiatives risked "pulling resources or capabilities away from NATO".
Stoltenberg said the right balance could be struck.
"Done in the right way, these efforts can make a contribution to fairer burden-sharing between Europe and North America," Stoltenberg told reporters earlier.
Stoltenberg has warned there was "no way" the EU could replace the transatlantic alliance in guaranteeing European security.
"It will be absolutely without any meaning if NATO and the EU start to compete," the former Norwegian premier told reporters on Tuesday.
"European allies are absolutely aware that the defence, the protection of Europe is dependent on NATO."
- Turkey row -
Potentially more serious is the festering row between the United States and Turkey over Ankara's "Operation Olive Branch", launched last month against the Syrian Kurdish People's Protection Units (YPG).
While Turkey views the YPG as a "terrorist" group, the United States has been working closely with the militia against the Islamic State group in Syria and giving it weapons, infuriating Ankara.
Mattis is to meet his Turkish counterpart on the sidelines of the meeting on Wednesday and Stoltenberg welcomed the fact that Turkey and the United States were talking directly.
Stoltenberg said Turkey briefed NATO on its military operation. "I reiterate that NATO recognised that Turkey has serious security concerns but we expect them to act in a measured and proportionate way."