By Michelle Nichols

UNITED NATIONS (Reuters) - United Nations aid chief Stephen O'Brien told the Security Council on Wednesday that the "buck stops with you" when it comes to ending the nearly six year war in Syria and he is "incandescent with rage" that no action is being taken to do so.

O'Brien's monthly briefing to the 15-member council on the humanitarian aid situation in Syria sparked an angry exchange, pitting Russia against the United States, Britain and France.

"I call upon all council members who have operational military assets in Syria to take concrete steps to halt the aerial bombardment of civilian areas," said O'Brien, specifically slamming the government of Syrian President Bashar al-Assad and Russia for bombing the city of Aleppo.

Russia and China have protected Syria's government from Security Council action to try and stop the war, including vetoing a bid to refer the situation to the International Criminal Court. Russia has blocked five council resolutions.

U.N. Secretary-General Ban Ki-moon, who steps down at the end of the year after serving two five year terms, told Reuters on Friday that he deeply regrets the Syrian conflict has not been resolved.

"Aleppo has essentially become a kill zone," O'Brien told the 15-member body, adding that no U.N. aid had reached eastern Aleppo for four months. "Civilians are being bombed by Syrian and Russian forces, and if they survive that, they will starve tomorrow. The tactics are as obvious as they are unconscionable."

Aleppo, Syria's most populous city before the war erupted, is now divided into government- and rebel-held areas. Intense bombardment by Syrian and Russian warplanes has reduced the rebel-controlled east to ruins. Russia said on Tuesday it would extend a moratorium on air strikes on Aleppo into a ninth day.

Russian U.N. Ambassador Vitaly Churkin hit back at O'Brien, describing his remarks as "arrogant" and criticizing him for not talking about Russia's halt to air strikes in Aleppo.

"If we needed to be preached to we would go to a church," Churkin said. "Please leave this kind of a report for a novel you might write one day."

He also denied that Russian planes had dropped leaflets on eastern Aleppo - cited in the council by O'Brien and U.S. Ambassador Samantha Power - that warned people to leave or "you will be annihilated."

O'Brien responded: "Don't shoot the messenger." Several council members, including the United States, France and Britain, also jumped to the defense of O'Brien.

"What Russia really wants from the U.N. is credit," Power told the council. "You don't get congratulations and get credit for not committing war crimes for a day or a week."

Syria's war pits Assad, backed by Russia, Iran and Shi'ite Muslim militias from Lebanon, Iraq and Afghanistan against mostly Sunni Muslim rebel groups including some backed by Turkey, Gulf monarchies and the United States.

"I cannot help but be incandescent with rage. Month after month, worse and worse, and nothing is actually happening to stop the war, stop the suffering," O'Brien told the council.

"If you don't take action, there will be no Syrian peoples or Syria to save – that will be this council's legacy, our generation's shame," O'Brien said.

(Reporting by Michelle Nichols; editing by Grant McCool)