The U.N. Security Council has arrived in South Sudan to threaten an arms embargo and sanctions if the government rejects a plan to bring in another 4,000 peacekeepers.

The rare visit focuses on the council's decision to deploy the peacekeepers with a strengthened mandate to protect civilians after reports of rapes and attacks by government troops.

South Sudan is wary of giving the U.N. more authority and has called the plan a new colonialism.

U.S. Ambassador Samantha Power delivered a stern message on arrival, noting recent obstructions of U.N. work.

A South Sudanese official cut short the opening press conference.

The diplomats are expected to meet with President Salva Kiir and urge both sides to adhere to a fragile 2015 peace deal meant to end the country's civil war.