BRUSSELS/PARIS (Reuters) - France and Germany will agree to a U.S. plan for NATO to play a bigger role in the fight against Islamic militants at a meeting with President Donald Trump on Thursday, but insist the move is purely symbolic, four senior European diplomats said.

NATO Secretary General Jens Stoltenberg addresses a news conference ahead of leaders' meeting in Brussels, Belgium May 24, 2017. REUTERS/Hannibal Hanschke

The decision to allow the North Atlantic Treaty Organization to join the coalition against Islamic State in Syria and Iraq follows weeks of pressure on the two allies, who are wary of NATO confronting Russia in Syria and of alienating Arab countries who see NATO as pushing a pro-Western agenda.

“NATO as an institution will join the coalition,” said one senior diplomat involved in the discussions. “The question is whether this just a symbolic gesture to the United States. France and Germany believe it is.”

All 28 NATO ambassadors agreed in Brussels on Wednesday on NATO joining the coalition, paving the way for leaders to endorse the decision on Thursday, a second diplomat said.

Flying to the NATO meeting in Brussels with Trump, U.S. Secretary of State Rex Tillerson said on Wednesday it would be an important step for the organization to join the U.S.-led, 68-nation coalition.

“I think they’re going to support NATO joining and becoming a formal member,” he said, referring to “a couple of countries that are still thinking it over” but not giving details.

Trump has said he wants to focus on fighting Islamic terrorism and, in a brief encounter with the Belgian prime minister, referred to a suicide attack claimed by Islamic State that killed 22 people in Manchester on Monday.

“It’s a horrible situation ... unthinkable. But we will win,” Trump said. “We are fighting very hard, doing very well under our generals ... We will win this fight.”

MESSAGE OF UNITY

A senior French diplomat said Paris was ready to accept NATO joining the coalition fighting Islamic State, but that its role would be limited to training and intelligence, things allies were already involved in.

U.S. and other European officials want to show Trump, who called NATO “obsolete” because he said it was not doing enough against terrorism, that the alliance is responding.

While Islamic State is on the verge of defeat in its Iraqi stronghold of Mosul and bracing for an assault against its de facto capital in Raqqa, Syria, U.S. officials are concerned fleeing militants could leave a vacuum that could prompt Arab tribal fighters to turn on each other to gain control.

All 28 NATO allies are members of the coalition, but the alliance as a formal member could become more involved, contributing equipment, training and the expertise it gained leading nations against al Qaeda and the Taliban in Afghanistan.

NATO Secretary-General Jens Stoltenberg has also made the case for a non-combat role for the alliance in Syria and Iraq.

“NATO joining the coalition will also provide a better platform for coordinating the activities of NATO allies ... in the fight against terrorism,” Stoltenberg said.

“It sends a strong and clear message of unity in the fight against terrorism and especially in light of the terrorist attacks in Manchester,” he said.

Some allies including Britain were keen for NATO to do even more, for example using its AWACS surveillance planes over Syria and running command-and-control operations.

German and French opposition means that for the moment, only one plane will watch over Syria from NATO-ally Turkey’s airspace to provide air traffic information to improve safety for planes.

French government spokesman Christophe Castaner told reporters that President Emmanuel Macron would speak to Trump at their lunch in Brussels on Thursday and that he understood Trump’s call for a greater NATO role in Syria and Iraq.

“The president will say that he is attentive to this (Trump’s call), but to make clear that it is not about transforming NATO into the sole strike force against Islamic State,” Castaner said.