UN Secretary-General Ban Ki-moon (right) prepares ahead of the opening ceremony of the International Humanitarian Pledging Conference for Syria at Bayan Palace on the outskirts of Kuwait City on Jan. 30, 2013. (STEPHANIE MCGEHEE/REUTERS)

U.N. Secretary General Ban Ki-moon opened a donor conference for humanitarian aid for Syria on Wednesday by calling on all parties, especially the government of President Bashar al-Assad, to end the violence in the nearly two-year old conflict that, by United Nations estimates, has left at least 60,000 dead.

“The situation in Syria is catastrophic and getting worse by the day,” the U.N. chief said at the conference, which is being held in Kuwait and has drawn representatives from more than 60 countries as well as several non-governmental organizations.

“I appeal to all sides, and particularly the Syrian Government, to stop the killing. In the name of humanity: Stop the violence.”

The conference aims to raise $1.5 billion to address a humanitarian crisis that is spinning out of control. Ban noted at the conference that more than 700,000 Syrians have fled the country and roughly 10 percent of the population has become internally displaced. He estimated that some 4 million Syrians, half of them children, are in need of assistance. 

Shortly after the session got underway, the United Arab Emirates, Saudi Arabia and conference host Kuwait each pledged $300 million in aid.

A look at the Syrian uprising nearly two years later. Thousands of Syrians have died and President Bashar al-Assad remains in power, despite numerous calls by the international community for him to step down.

President Obama, who has been under political pressure to do more to stem the violence, announced Tuesday that the United States will provide $155 million in new humanitarian assistance to Syrians, nearly doubling the American commitment. Obama said the assistance would go toward providing medicine, food, and clothing and blankets as winter approaches.

U.N. officials said the United Nations is seeking to provide at least $1.5 billion in relief. Officials warned Monday of increasingly desperate conditions for about 4 million Syrians inside the war-torn country and about 650,000 in refu­gee camps outside.

On Tuesday, at least 65 people were found dead in the contested Syrian city of Aleppo, many of them bound and shot execution-style, according to opposition activists. The discovery served as a grim reminder of the country’s bloody descent into violence and the failure of diplomatic efforts to stop the killing.

Opposition activists said it was not clear who had carried out the killings, when they happened or why. Some activists said they believed that the Syrian military or a pro-government militia was responsible and suggested that the victims may have been political detainees.

The killings provided a sobering backdrop to stalled diplomatic efforts to end the fighting. Lakhdar Brahimi, the U.N.-Arab League envoy to Syria, issued an impassioned appeal to members of the U.N. Security Council, asking them to put aside their differences and take firmer action to help stop the bloodshed.

Syria, Brahimi warned, was on the verge of disintegrating.

“I’m sorry if I sound like an old broken record,” Brahimi told the council during a closed session, according to notes of his briefing obtained by The Washington Post. “The country is breaking up before everyone’s eyes.”

Timeline: Major events in Syria’s tumultuous uprising that began in March 2011.

Brahimi told the council that the effort to persuade the warring factions to enter political talks had run aground, with the Syrian government and the armed opposition unwilling to speak to each other. Meanwhile, key regional powers have picked sides in the conflict, he said, transforming Syria into a “playground for competing forces.”

Opposition groups said they expected the number of known dead in the Aleppo killings to increase.

A video posted online Tuesday showed many bodies — apparently including those of some teenagers — lying on the muddy banks of the Quweiq River in the rebel-held Bustan al-Qasr neighborhood of southwestern Aleppo. Bustan al-Qasr has been the site of heavy fighting in recent days as the Syrian military has launched several attacks to retake the neighborhood.

Lynch reported from the United Nations. Ahmed Ramadan in Beirut contributed to this report.