“It’s hard to find a place where there is conflict and Iran isn’t in the middle of it,” Ms. Haley said at a news conference. “We think they’ve been ignored and given a pass for too long, and we think it’s time for Iran to stand up and explain themselves.”

At the Security Council, Mr. Trump could face stiff resistance not only from opponents of the United States, but also from allies like Britain and France, who were strongly opposed to the administration’s abrupt withdrawal from the Iran nuclear agreement they helped negotiate with the Obama administration.

Though many are highly critical of Iran’s involvement in wars in Yemen and Syria, few consider the country to be the global menace the United States portrays it to be.

“I understand that there are some members who find that uncomfortable to talk about,” Ms. Haley said. “I personally think that when we talk about things that are uncomfortable at the Security Council, good things happen.”

Mr. Trump will also have to contend with the arcane system of rules and protocols that govern conduct within the typically staid Security Council chamber. Sessions are normally tightly scripted affairs, with ambassadors rarely straying from prepared remarks.