United Nations Deputy Secretary General Jan Eliasson says the Syrian conflict is a "bleeding wound" that has "hurt" the reputation of the world body.
He said the fact that global powers have not been able to unite to stem the country's bloodshed, which has claimed more than 70,00 lives so far, has damaged the UN's global standing.
"I must very honestly confess that it has hurt the reputation of the United Nations in the world that we haven't seen action stopping this horrible war which has been going on now for over two years," Mr Eliasson told The Straits Times during a visit to Singapore earlier this month.
"For this civil war to end it is necessary for the Security Council to establish unity."
Mr Eliasson, who is next in charge after Secretary General Ban Ki Moon, lamented the absence of a UN Security Council resolution on the Syrian conflict, which began in March 2011.
In July, Russia and China, two permanent members of the Security Council, vetoed plans to impose non-military sanctions against Syrian President Bashar Assad's regime to halt its brutal crackdown on protesters.
Russia argued that the sanctions could pave the way for military intervention against Assad, who is a key ally of Moscow.
Mr Eliasson, who heads UN peacekeeping efforts, said the lack of a unified UN voice has greatly reduced the "muscular power" of the world's "best negotiators", such as former secretary general Kofi Annan, to press for a political solution between the Syrian regime and the opposition.
A month after the Security Council failed to secure a resolution on Syria, Mr Annan quit as the UN and Arab League's special peace envoy to the war-ravaged country. He cited a "lack of unity" among the members of the Security Council as a factor.
Mr Lakhdar Brahimi, an 79-year-old Algerian diplomat who took over the role from Mr Annan, is also "coming to the end of his patience", Mr Eliasson said.
During his three-day trip to Singapore earlier this month, the Deputy Secretary General delivered a lecture to students at the Lee Kuan Yew School of Public Policy in which he described Syria as "a bleeding wound" for the UN.
While a political solution to the crisis remains elusive, Mr Eliasson said the global organisation has been providing aid to millions of Syrians displaced by the war. Around 1.2 million people have fled to Lebanon, Jordan, Iraq and Turkey, he added, increasing the risk of "a regional conflict".
"I certainly hope...that the Security Council will see the risks of this already huge tragedy turning into an even larger one with the conflict, or parts of the conflict, spreading into neighbouring countries."
Mr Eliasson made the comments before news broke that Israel had carried out air strikes in and around Syrian capital Damascus on May 3.
The attacks were aimed at stopping Iranian weapons from reaching Hezbollah in Lebanon, Israeli sources told news agencies.
On May 11, twin car bombs killed at least 20 people near Turkey's border with Syria, heightening fears that the conflict could spread throughout the region.