Mirgayas Shirinskiy, 62, was found dead in the swimming pool at his home in the Sudanese capital. He was the fourth Russian envoy to die on the job in the past eight months.
Russian President Vladimir Putin leads the tributes to veteran diplomat Vitaly Churkin who died a day before his 65th birthday in New York.
The action marked the first time the United States has sanctioned Syrian forces officials for the regime's use of chemical weapons, according to a Treasury Department statement.
Antonio Guterres, former head of the UN refugee agency, took over Ban Ki-moon's post on New Year's Day with a promise to shake up the world body.
Measure drafted by Canada passes by a vote of 122 to 13 in the 193-nation assembly, with 36 abstentions. Russia, Iran and China oppose the resolution.
Staffan de Mistura also plans to hold meetings with US President-elect Donald Trump's transition team.
Aleppo is under heavy bombardment, as Syrian regime forces backed by Russia press a large-scale offensive to recapture all of the city from opposition forces.
Rebel groups in the area, including Fastaqim and Nusra Front, have united under one banner called the "Army of Aleppo" to fight regime forces in east Aleppo.
UNICEF director says school compound was "repeatedly attacked," adding that it may be the deadliest attack on a school since the Syrian conflict began more than five years ago.
European countries and the United States are shifting toward a tougher line on Russia over its actions in Syria and have suggested that sanctions could be imposed.
The sixth secret vote unanimously confirmed Antonio Guterres as a clear candidate for the next chief as none of the five permanent UN Security Council veto powers voted against him.
US Ambassador Samantha Power accused Russia of "barbarism" during the Security Council emergency meeting on Syria.
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