BRUSSELS — U.S. Defense Secretary Ash Carter predicted on Thursday that recent U.S.-led efforts to accelerate the fight against the Islamic State group would produce “tangible gains” in Iraq and Syria by March, even as he urged coalition partners to expand and deepen their military contributions.

Carter expected that defense ministers from more than two dozen countries would endorse a new U.S. plan for taking on IS. The ministers planned a joint statement after their meeting at NATO headquarters.

In public remarks at the start of the session, Carter cast the talks as an historic effort to hasten the demise of IS, which has proved resilient in Iraq and Syria and is spreading to Afghanistan, Libya and elsewhere in the greater Middle East.

“This ministerial marks the beginning of a new stage in the coalition campaign to defeat ISIL,” Carter said, using a common acronym for the militants. He suggested that countries not answering his call to do more may regret their choice when the struggle is over.

“We will all look back after victory and remember who participated in the fight,” he said.

In Munich, Germany, U.S. Secretary of State John Kerry was trying on Thursday to find a way to halt what amounts to a parallel war in Syria. Five years of civil war have pitted President Bashar Assad’s government, backed by Russia and Iran, against an array of weakened opposition groups, some supported by the United States.