WASHINGTON — The United States banned the export of weapons and defense services to South Sudan on Friday in a reflection of the Trump administration’s growing frustration over that nation’s grinding civil war.
The ban has little practical effect, since the United States does not sell weapons to the country. But the announcement on Friday was the first step in a broader effort to cut off weapons to a conflict that has put 1.5 million people on the brink of starvation.
Heather Nauert, the State Department’s spokeswoman, said the administration would soon resume a push begun under President Barack Obama for the United Nations Security Council to impose a global arms ban against South Sudan.
“The message must be clear: The United States, the region and the international community will not stand idly by as innocent South Sudanese civilians are murdered,” Ms. Nauert said.
Nikki R. Haley, the American ambassador to the United Nations, called for an arms embargo last week. Ms. Haley visited South Sudan in October, and the State Department is largely taking its cues on the issue from her.
“I was pleased to see the administration move in this direction, and I think Nikki Haley has led that movement,” said Linda Thomas-Greenfield, who was assistant secretary of state for African affairs during the Obama administration.
The Obama administration helped midwife the birth of oil-rich South Sudan as an independent nation in 2011. When civil war erupted there in 2013 after President Salva Kiir, an ethnic Dinka, accused his former deputy, Riek Machar, an ethnic Neur, of fomenting a coup, the United States initially sided with Mr. Kiir.
But as government forces abrogated or ignored a peace agreement and a series of cease-fires, Washington’s frustration with Mr. Kiir grew. In the latest example, the country’s military forces captured the rebel-held town of Lasu in December, creating yet another flow of refugees, despite a unilateral cease-fire that Mr. Kiir had declared in May.
Tens of thousands of people have died in the conflict, more than two million have fled to neighboring countries and almost two million more are internally displaced, despite the presence of 17,000 United Nations peacekeepers in the country.
The crisis comes as a drought in nearby Somalia, Ethiopia and Kenya has put millions more at risk of starvation. Some top officials close to Mr. Kiir have been placed under sanctions by the United States, and on Monday the African Union expressed support for imposing sanctions on leaders who are violating cease-fires in South Sudan.
Uganda, which sent troops to fight on the side of the government of South Sudan in the early stages of the war, is still feeding the conflict with weapons, said Richard Downie, deputy director of the Africa program at the Center for Strategic and International Studies, who visited the region in January. Uganda receives considerable security and development assistance from the United States.
“So we give Uganda all this aid, and yet it’s been fueling the conflict, so they’ve been playing us,” Mr. Downie said.
Neither Ms. Thomas-Greenfield nor Mr. Downie believed the United Nations would vote to impose an arms embargo, since Russia and China tend to oppose such efforts as meddlesome. And even if an embargo were passed, neither thought it would do much good.
“An arms embargo is not going to change anything, but there are not a lot of good options out there,” Mr. Downie said.
Ms. Thomas-Greenfield said there was not much else the United States could do. “I still think we should try for an embargo,” she said.
Also Friday, the Treasury Department imposed sanctions on six people and seven companies associated with Hezbollah, the Iranian-backed political and military organization that is deeply entwined in Lebanon’s government and backs President Bashar al-Assad of Syria in the civil war in that country.
The designation is intended not only to punish Hezbollah but also to signal that the United States’ efforts against Iran go beyond the Trump administration’s focus on renegotiating the 2015 Iran nuclear agreement.