An F/A-18F Super Hornet lands on the USS Dwight D. Eisenhower in the Mediterranean Sea on July 6. (Alberto Pizzoli/AFP/Getty Images)

Defense Secretary Ashton B. Carter will gather defense ministers from allied nations this week to plan what officials hope will be the decisive stage in the campaign against the Islamic State, even as political upheaval and terrorist attacks strain the U.S.-led coalition battling the group.

At Wednesday’s meeting at Joint Base Andrews outside Washington, Pentagon officials will present plans for upcoming battles in Iraq, where local forces are preparing to confront militants in the city of Mosul, and in Syria, where U.S.-backed fighters hope to eventually isolate militants in their de facto capital of Raqqa.

As they have in the past, senior American officials will press visiting ministers to commit additional troops and assets to the campaign, with a special focus on resources earmarked for efforts to stabilize and rebuild areas reclaimed from the Islamic State, also known as ISIS or ISIL.

“It’s going to be, ‘Here’s what we need,’ ” a U.S. defense official said, speaking on the condition of anonymity to preview this week’s discussions. “So they can go back to their countries and start working on what they’re going to contribute.”

The discussions, which will be followed on Thursday by a larger meeting hosted by Carter and Secretary of State John F. Kerry, mark the first summit on the Islamic State since Britain’s vote to leave the European Union and the failed coup attempt in Turkey. Those events have intensified anxiety about the ability of Europe and its allies to manage migrant flows, rising nationalism and other shared threats across the region.

Bilal Saab, a scholar at the Atlantic Council in Washington, said the differing political priorities of the more than 30 nations gathered in Washington this week have at times been a drag on the international effort against the Islamic State. “Every country is struggling with their own domestic issues, and so to coordinate and speak with one voice is still the greatest challenge,” Saab said.

Two years after Islamic State militants declared their caliphate across Iraq and Syria, the United States continues to shoulder the bulk of outside military operations against the extremist group. Since the summer of 2014, the United States has conducted more than 10,500 airstrikes in Iraq and Syria; allied nations together have launched only 3,200.

While the Obama administration has had some success in coaxing allies to increase their troop contributions, the U.S. footprint in Iraq, at around 6,000, remains by far the largest. Italy, with the second largest, has personnel totaling about 900 in Iraq.

The United States is the only nation with a significant troop presence in Syria, with about 300 advisers working with Kurdish and Arab fighters there.

Since the early days of the war, Iraq’s Persian Gulf neighbors, tied up in a separate campaign in Yemen, have contributed little military power to the fight in Iraq and Syria.

While Jordan has hosted American efforts to train Syrian opposition fighters, the kingdom is facing security threats of its own and, like Lebanon and Turkey, is grappling with a crush of displaced Syrians.

Speaking with reporters about this week’s meetings, Brett McGurk, President Obama’s envoy to the coalition battling the Islamic State, said the group of countries had proved resilient. “It’s strong, it’s united, it’s organized,” he said.

But even Washington’s closest allies have made only limited contributions as they have sought to match their smaller militaries to an array of challenges from West Africa to Afghanistan.

France stepped up its operations last year after Islamic State supporters launched coordinated attacks in Paris. After last week’s bloody attack during a Bastille Day celebration in Nice, French President François Hollande vowed to redouble military efforts and said France‘s sole aircraft carrier would return to the gulf to continue striking militant targets.

Hollande, like other European leaders, is under intense political pressure to show he can keep his people safe, even as divisions about Europe’s future threaten to hinder security efforts across the continent.

Britain, which has more than 250 advisers in Iraq, has promised to sustain its efforts against the Islamic State. But officials are at the same time racing to determine how even the most basic aspects of governance and international cooperation will work in the wake of Britons’ June vote to leave the E.U.

NATO member Turkey, whose long border with Syria has made it a crucial coalition member, is reeling, meanwhile, in the wake of last week’s failed coup attempt.

Turkish officials are promising that recent turmoil will not affect the country’s Syria policy. But it could serve to add friction to Turkey’s already fraught ties with the United States.

“These are all critical vulnerabilities that if they’re not addressed . . . the happy talk could come undone,” said Linda Robinson, a scholar at the Rand Corp.

U.S. officials said the discussions at Andrews will focus on efforts to aid residents affected by fighting against the Islamic State, especially those from Mosul, after the fighting ends. After the recent victory in Fallujah, residents struggled to survive in desert camps lacking basic necessities.

To avoid a repeat of past problems, the Pentagon will ask allied nations to volunteer engineers and police trainers. The hope is that outside assistance will help the Iraqi government, already grappling with low oil revenue and popular discontent, prevent extremist groups from regaining a foothold.

While Islamic State defenses have folded relatively swiftly in some areas, Robinson said the United States will need to ensure longer-term stability not just by soliciting pledges from allies but also by ensuring that assistance is properly provided.

The challenge now, she said, is to “make sure the military gains are not outpacing what you need to do on stabilization and political solutions.”

Karen DeYoung in Washington and Thomas Gibbons-Neff in Ankara, Turkey, contributed to this report.