South Sudan's army has shot down a United Nations helicopter, killing all four Russian crew members.
A South Sudan military spokesman said troops mistook the helicopter for an aircraft supplying weapons to rebels.
U.N. Secretary General Ban Ki-moon
strongly condemned the attack, saying the U.N. helicopter was clearly marked. He called on the government to immediately carry out an investigation.
The United Nations says the flight was on a reconnaissance mission when it went down Friday in the eastern state of Jonglei. An initial U.N. report said the helicopter had simply crashed.
The president of the U.N. Security Council, Moroccan Ambassador Mohammed Loulichki, says the shooting is a grave violation of the U.N.'s mandate in South Sudan and jeopardizes the U.N. operation there, known as UNMISS
"The members of the Security Council strongly deplore the shooting down in Jonglei state South Sudan on December 21, 2012, by the Sudan People's Liberation Army on UNMISS helicopter performing a reconnaissance flight to the area with four Russian crew members all of whom were confirmed dead," said the ambassador.
In separate development Friday, the United Nations says four peacekeepers died in South Sudan's northern neighbor, Sudan. A spokeswoman said one peacekeeper shot three others before killing himself at a U.N. site in Sudan's western Darfur region. She did not give further details of the incident or the nationalities of the peacekeepers involved.
Some information for this report was provided by AP, AFP and Reuters.