* UN's Ban urges Syria's Assad to heed suffering of people
* Decries "horrors" in Syria, urges end to civil war
* $1.5 billion pledged aid to cover next six months -Ban
* Appeal follows reported massacre of 65 people in Aleppo
* Damascenes doubtful necessary aid will reach them
* Crisis escalating as more flee, war damage extensive (Adds UN leader Ban's appeal to Assad)
By Sylvia Westall
KUWAIT, Jan 30 Donor countries have pledged more than $1.5 billion to aid Syrians stricken by civil war, U.N. Secretary-General Ban Ki-moon said on Wednesday after warning that the conflict had wrought a catastrophic humanitarian crisis.
In a pointed message for Syria's leader, Ban told a fund-raising conference that President Bashar al-Assad bore primary responsibility to stop his country's suffering after nearly two years of conflict that have cost an estimated 60,000 lives.
"Every day Syrians face unrelenting horrors," Ban told the gathering in Kuwait, adding these included sexual violence and arbitrary killings. Sixty-five people were shot dead execution-style in Aleppo on Tuesday, opposition activists said.
"We cannot go on like this.... He should listen to the voices and cries of so many people," Ban said.
"I appeal to all sides and particularly the Syrian government to stop the killing ... in the name of humanity, stop the killing, stop the violence."
Ban said the one-day conference had exceeded the target of $1.5 billion in pledges. About $1 billion is earmarked for Syria's neighbours hosting refugees and $500 million for humanitarian aid to Syrians displaced inside the country.
The $500 million would be channelled through U.N. partner agencies in Syria. and the entire aid pledge would cover the next six months, Ban said.
But in the Syrian capital Damascus, the thud of artillery drowned out any optimism on the streets. Asked about the aid promises, Damascenes were uninterested or despairing.
"Where's the money going to go to? How does anyone know where it's going? It all seems like talk," said Faten, a grandmother from a middle-class family in the capital.
Another middle-class Damascene, a woman in her 70s who asked not to be named, said the money would not make it to Syrians.
"Tomorrow all that money will get stolen. (The middlemen) steal everything. If they could steal people's souls, they would. I wouldn't count on the money," she said.
The oil-rich Gulf Arab states of Kuwait, Saudi Arabia and the United Arab Emirates each promised $300 million at the meeting. Its 60 participants included Lebanon, Jordan, Iran, Tunisia, the United States, Canada, Russia, China, Japan, South Korea, Turkey and a number of European countries.
But relief groups say that converting promises into hard cash can take much time, and one of them said on Tueday that aid now reaching Syria was not being distributed fairly, with almost all of it going to government-controlled areas.
"GETTING WORSE EVERY DAY"
Ban said that much more remained to be done to address Syria's humanitarian emergency. "The situation in Syria is catastrophic and getting worse every day."
Four million Syrians inside the country need food, shelter and other aid in the midst of a freezing winter, and more than 700,000 more are estimated to have fled to countries nearby.
U.N. humanitarian chief Valerie Amos said that Syrian agriculture was in crisis, hospitals and ambulances had been damaged and even painkillers were unavailable.
Freezing, snowy winter weather had made matters worse, and people lack warm clothes, blankets and fuel, with women and children particularly at risk, she said, adding:
"We are watching a human tragedy unfold before our eyes."
Kuwait's emir, Sheikh Sabah al-Ahmad al-Sabah, told the meeting "horrifying reports" of violence had raised questions about Syria's future and relief efforts had to be redoubled.
Syrian opposition activists said at least 65 people were found shot dead with their hands bound in the embattled northern city of Aleppo on Tuesday, the latest reported massacre over the course of 22 months of conflict.
They blamed militiamen loyal to Assad, while the government blamed the Islamist rebel Nusra Front. It was impossible to confirm who was responsible given Syria's restrictions on access for independent media.
More than 60,000 people have been killed in all, according to a U.N. estimate, since the conflict began as a peaceful movement for democratic reform and escalated into an armed rebellion after Assad tried to crush the unrest by force.
Diplomacy to halt the war has been stymied by deadlock in the U.N. Security Council between Western powers, who want Assad to quit as part of a democratic transition, and Russia, a close Assad ally that rejects outside interference in Syria.
And the fighting is largely stalemated in Syria, with rebels holding swathes of the north and east but unable to take key cities because of the government's air power and superiority in heavy weapons.
King Abdullah of Jordan told the donors' meeting Syrians had taken refuge in his country in their hundreds of thousands but Amman's ability to help was at its limits. "We have reached the end of the line, we have exhausted our resources," he said.
Iran, a staunch supporter of Assad, said the blame for the humanitarian crisis lay with rebel fighters who had come to Syria from abroad.
Iranian Foreign Minister Ali Akbar Salehi said the government and its Syrian opponents should "sit and talk and form a transitional government".
"Those who are causing these calamities are mercenaries who have come to Syria from outside the country," he said. (Reporting by Sylvia Westall, Ahmed Hagagy, Sami Aboudi, Mahmoud Habboush and Mirna Sleiman; Writing by William Maclean; Editing by Mark Heinrich)