Secretary of State Rex Tillerson will lead a two-day gathering of a global coalition focused on fighting the Islamic State militarily and starving it of money, weapons and fighters. (Joshua Roberts/Reuters)

The Trump administration has invited more than 60 nations and international organizations to Washington later this month for a strategy session on how to counter the Islamic State after a widely expected U.S.-backed military assault on the extremists’ home base.

Secretary of State Rex Tillerson will lead a two-day gathering of a global coalition focused on fighting the group militarily and starving it of money, weapons and fighters.

The session is an important signal that the new administration intends to maintain leadership of a sprawling diplomatic effort begun by President Barack Obama in 2014, despite Trump’s scathing assessment of Obama’s approach to the Islamic State during the presidential campaign.

The March 22-23 meeting will be the largest since the inaugural session and comes as the Islamic State appears to be losing ground militarily.

“We are at an important stage of the fight against ISIS,” the State Department said in announcing the session, which it said would “accelerate international efforts to defeat ISIS in the remaining areas it holds in Iraq and Syria and maximize pressure on its branches, affiliates, and networks.”

The Trump administration had said it would retain Obama’s top official in charge of what was formerly called the Global Coalition to Counter ISIL but had not spelled out its goals for the group of 68 countries and international organizations.

The Trump administration has substituted its preferred acronym, ISIS, in the global coalition’s name but left the organization’s structure and focus intact. The revised State Department Web page for the coalition also stripped out mention of Obama and former secretary of state John F. Kerry but kept language stressing that “there is a role for every country to play in degrading and defeating” the militants.

The Islamic State is loosely based in Raqqa, Syria, and holds part of the strategic Iraqi city of Mosul but has been routed from other territory. If defeated as an army, however, the Islamic State would retain power to launch attacks and spread its message online.

“While many challenges remain, ISIS is cornered in Mosul and increasingly isolated in Raqqa,” the State Department said. “This . . . meeting is a key moment to set ISIS on a lasting and irreversible path to defeat.”

It is also Tillerson’s first opportunity to demonstrate commitment to the idea of a collective response to the Islamic State and to ask other nations for help. The coalition includes military partners and nations that support diplomatic and humanitarian efforts through donations of money, expertise and other resources.

“It’s consistent with what the president talked about in terms of burden-sharing and asking other countries to carry their load,” said one U.S. official who spoke on the condition of anonymity to describe U.S. goals for the meeting ahead of its announcement. “They need to hear that from the new secretary of state” and know that “this was not on autopilot. He decided to do this.”

The coalition’s future is a question that involves the new politics in Washington and the eroding military power of the Islamic State. Diplomats from some of the countries involved have questioned whether the coalition would be disbanded if the extremist group is routed from Raqqa.

One European diplomat said the expected military assault in Raqqa would leave no clear physical battlefield to confront the Islamic State, despite continued humanitarian and political problems in Iraq and Syria.

Another official said that although the upcoming meeting is not a fundraising conference, the coalition aims to raise about $1.5 billion for humanitarian and other efforts in the near term.

Trump campaigned on a pledge to expand what he called a weak and indecisive fight against the militants in Syria, Iraq and beyond, but his strategy thus far is not markedly different from Obama’s.

A revised Pentagon plan for Raqqa calls for significant U.S. military participation, including increased Special Operations forces, attack helicopters and artillery, according to U.S. officials. It also would send arms to the main Syrian Kurdish and Arab fighting force on the ground.

Although Americans would not be directly involved in ground combat, the proposal would allow them to work closer to the front lines.

Russia is not a member of the diplomatic coalition, although it is a dominant military presence in Syria in support of President Bashar al-Assad’s forces.

Trump has raised the prospect of the United States and Russia collaborating to fight Islamic State militants in Syria, and he and Russian President Vladi­mir Putin discussed possibilities in a phone call in January, according to the White House. But the issue is complicated by political fallout from Russia’s alleged interference in the 2016 presidential election, and Defense Secretary Jim Mattis has said that discussion of any broad cooperation is premature.

Another senior U.S. official said this week that cooperation seemed more likely if a Russian-guaranteed cease-fire proved durable.

“There was a lot of this talk a few weeks ago,” the official said. “Now it is in abeyance.”

When hopes for the cease-fire were high, Tillerson had asked for an economic breakdown of Syria — how the oil, water and agriculture resources were divided in the country. The idea was that the Trump administration might be able to work with the Russians to carve out autonomous territories that could survive with little or no connection to Damascus, that official said.

“You could have regions that would be able to sort of exist, and maybe they would not be in kinetic opposition to the regime. Instead there would be a live-and-let-live scenario.”

But as the Russians have been unable to deliver on the cease-fire, such hopes have given way to more practical realities that the Obama administration faced, the official said.

Greg Jaffe contributed to this report.