Members of the coalition fighting the Islamic State extremist group pledged Thursday to "accelerate and intensify" their campaign, while US Secretary of Defence Ashton Carter criticized Russia for becoming a "participant" in Syria's civil war.
Washington has sought in recent weeks to ramp up contributions from the roughly 60 countries supporting the air campaign against Islamic State in Syria and Iraq. Participants include NATO members France, Britain and Turkey, as well as several regional powers.
"Significant work remains to be done to ensure the lasting defeat of ISIL/Daesh and the restoration of stability in Iraq and Syria," the defence ministers of 28 coalition countries said in a statement, using alternative names for the extremist group.
The campaign is focusing on recapturing Mosul, Iraq's second-largest city that was taken by Islamic State, and al-Raqqa, the group's stronghold in Syria.
Carter spoke of new efforts to crack down on the group's financial capabilities, as well as plans to deploy Iraqi troops in the north, for the attack on Mosul. The ministers were also updated on Italian planning to tackle Islamic State "metastases" in Libya, he said.
The ministers called on those states playing a "counterproductive role" in the fight against the Islamic State to act more constructively, without mentioning Russia by name.
Carter accused Moscow of making a "strategic mistake" by failing to target Islamic State, as it had promised when it launched its own bombing campaign, and said Russia had instead become a "participant in the civil war in Syria."
The coalition is operating in parallel with diplomatic efforts to bring about an end to the near five-year conflict in Syria, with the latest round of talks taking place in Munich on Thursday.
"ISIL must be defeated, will be defeated, whatever happens with the Syrian civil war," Carter said.
During the Brussels meeting, he also held talks with Saudi Defence Minister Mohammad bin Salman. The kingdom, along with Bahrain and the United Arab Emirates, has announced its willingness to send ground troops to fight the Islamic State.
"The kingdom is ready to carry out all missions, whether air missions or land," said General Ahmed Asiri, an advisor to the Saudi defence ministry, in comments carried by the state-owned broadcaster Al Arabiya on Thursday.
But Carter said the offer of ground troops ran counter to the coalition's approach, which focused instead on enlisting "capable and motivated local forces.
"Territory retaken from ISIL has to be occupied and governed by people from are who are from that area and want to live there," the US defence secretary noted.
An overall 49 countries were invited to the talks, including all NATO members.
The military alliance is not involved in the campaign, but agreed at earlier talks Thursday to provide its surveillance planes to allies, to free up their national resources for operations over Syria and Iraq.
"The decision will increase the ability of the coalition to degrade and destroy the terrorist group ISIL, which is our common enemy," said NATO Secretary General Jens Stoltenberg.
Other forms of NATO cooperation are also being explored, Carter said, pointing to the possible training of ground forces as an example.