UNITED NATIONS (Reuters) - After threatening South Sudan with a U.N. arms embargo to encourage steps toward peace, the United States wants to impose the measure, but the 15-member Security Council is split and Washington cannot even convince ally Japan.

United States Ambassador to the United Nations Samantha Power addresses media at the United Nations in Manhattan, New York City, U.S., December 19, 2016. REUTERS/Andrew Kelly

U.S. frustration with Tokyo’s resistance to an embargo and additional targeted sanctions spilled over on Monday when Samantha Power, the U.S. Ambassador to the United Nations, publicly questioned the reluctance of Japan, which last month deployed troops to a U.N. peacekeeping mission in South Sudan.

“It’s a highly questionable logic to think that the way to keep your peacekeepers safe is to not support an arms embargo,” Power told reporters.

“Why would it be good for your peacekeepers to have a government whose people are starving spend what little money it has on weapons – large weapons systems – instead of on food?” she said. “It is in everyone’s interest, including the peacekeepers, for there to be fewer heavy weapons.”

U.N. diplomats, speaking on condition of anonymity, said Japan privately expressed displeasure, describing Power’s remarks as “not helpful and counterproductive.”

Political rivalry between South Sudan President Salva Kiir, an ethnic Dinka, and his former deputy Riek Machar, a Nuer, led in 2013 to civil war that often has followed ethnic lines. The pair signed a peace deal last year, but fighting has continued. Machar fled in July and is now in South Africa.

U.N. peacekeepers have been in South Sudan since the nation gained independence from Sudan in 2011, and there currently are some 13,700 U.N. troops and police in the country.

Secretary-General Ban Ki-moon on Monday told the Security Council that he feared genocide was about to start in South Sudan unless immediate action is taken, renewing his months-old plea for an arms embargo.

Japanese Defence Minister Tomomi Inada, though, suggested on Tuesday that now was not the right time for an arms embargo and further sanctions.

To be adopted, a resolution needs nine votes and no vetoes. Diplomats say that so far seven members were in favor, with the remaining eight planning to abstain or vote no.

Council veto powers Russia and China are skeptical that an arms embargo would achieve much in a country awash in weapons, but diplomats did not expect them to block the measure.

They said lobbying by the United States and other Western council members has focused on Japan and African members Senegal and Angola. Power wants to put the measure to a vote by the end of the year, and she appealed on Monday for her colleagues “to prepare to vote your conscience.”

“Arms embargo, probably it’s not the answer; we want answers to the situation in South Sudan,” Angola’s U.N. Ambassador Ismael Abraao Gaspar Martins told reporters. “It may not be respected, and we create other problems.”