NATO member states are expected to formally join a US-led coalition against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) armed group in Syria and Iraq, according to several diplomatic sources.
The decision by the North Atlantic Council, the highest decision-making body within NATO, is expected to be officially announced at a meeting of the alliance's leaders on Thursday.
"The NATO (member state) ambassadors decided this evening an action plan on terrorism for the summit. It includes the accession of NATO to the global coalition against IS," one diplomat told the AFP news agency on Wednesday, using a different name for ISIL.
The decision is mainly political because all 28 NATO member states are already individually part of the coalition, with some only taking part in support roles.
It comes on the back of pressure from US President Donald Trump, who has urged NATO members to do more in the fight against ISIL.
Diplomats said France and Germany will agree to the US plan, but insist the move is purely symbolic.
"NATO as an institution will join the coalition," one senior diplomat involved in the discussions told the Reuters news agency. "The question is whether this just a symbolic gesture to the United States. France and Germany believe it is."
The move will specifically involve an expansion of flights by NATO's AWACS surveillance aircraft currently supporting anti-ISIL operations in Syria and Iraq.
"This means that the AWACS will not just do airspace surveillance but airspace management," the diplomat said, asking not to be identified.
"They are going to coordinate the flights and direct airplanes over Syria and Iraq but only for flights which are not related to bombings."
Earlier on Wednesday, US Secretary of State Rex Tillerson said he expected NATO to join despite reservations by some members states which are fearful of getting dragged into another conflict.
Tillerson said that NATO's joining "would be a really important step" but that "there are a couple of countries that are still thinking it over."
"I have had meetings actually with one of those. I think they're going to support NATO joining and becoming a member of the ISIS fight," he told reporters travelling with Trump.
NATO chief Jens Stoltenberg said earlier that "many allies would like to see NATO as a full member of the coalition ... because it sends a strong message of unity".
He added that in light of Monday's attack in Manchester, "it is important to send this message of unity against terrorism".
Stoltenberg has previously stressed that there has been "no discussion at all of engaging NATO in a combat role" if it officially joins the coalition.
He also noted that besides sending a political signal of unity against terrorism, NATO's formal entry into the coalition would help allies improve coordination and provide better information flows.
At the Brussels meeting on Thursday, Trump is also expected to urge NATO members to increase defence spending to the target of two percent of a country's annual gross domestic product, as they agreed in 2014.
In return, the allies hope the US president will unequivocally state his support for NATO's mutual defence pledge, known as Article 5.
The alliance is also due to discuss whether to increase the number of soldiers in Afghanistan as Trump mulls over adding at least 3,000 troops in hopes of putting pressure on the Taliban to come to the negotiating table.
Many in Kabul, however, fear a troop increase will not help, and have instead urged more training and equipment.