The failure of the United Nations to take action over the Syrian government's deadly attacks on its own civilians has been "disastrous", the secretary general has said.
He added that the situation unfolding in the city of Homs, where shelling has resumed after at least 25 people were killed on Wednesday, was "unacceptable to humanity".
More than 200 people in Syria have been killed since last Friday, Amnesty International said on Thursday.
Ahead of rumours that the UN will take up a proposal by the Arab League for a joint mission to monitor the situation, Ban said that the current crisis could not be allowed to continue indefinitely.
"For too many months we have watched this crisis deepen," Secretary General Ban Ki-moon said at the UN headquarters in New York City.
"We have seen escalating violence, brutal crackdowns and tremendous suffering by the Syrian people.
"I deeply regret that the security council has been unable to speak with one clear voice to end the bloodshed."
He added that the veto on a resolution condemning the violence issued by Russia and China had been "disastrous for the people of Syria".
"It has encouraged the Syrian government to step up its war on its own people. Thousands have been killed in cold blood, shredding President Assad's claims to speak for the Syrian people."
Ban also warned that there would be "worse to come" unless the international community could take action.
"We stand ready to assist in any way that will contribute towards improvement on the ground and to the overall situation," he said.
The United States has also called for a "Friends of Democratic Syria" group, to show their support for the targets of the violence.
"We are, frankly, consulting with individual countries now about what that group, when it might be able to meet, what it might be able to do," a US state department official told CNN.
"But certainly one of the issues that we would like to see this group take up is the issue of humanitarian support for the people of Syria."
White House spokesman Jay Carney said President Assad had missed the opportunity for dialogue.
"Rather than take that opportunity, Assad brutally cracked down on his own people. We don't think that that opportunity is available any more," he said.
Dozens of people in Homs have been killed since the Syrian army resumed its assault on the city last week.
The Huffington Post UK has not been able to independently verify reports from the city, but evidence has emerged online illustrating the scale and horror of the violence.
Videos posted to YouTube by the British-born Syrian activist Danny Adbul Daymen appear to show a blasted landscape of civilian and residential buildings under apparently constant fire from rockets.
In one clip dated 8 February, which shows fire and smoke pouring from buildings, Daymen says:
"This is Homs, Baba Amr, you can see over there another rocket landed on one of the civilian's houses, this has been going on all day, since 5am.
"Why isn't the world helping us, where's the humanity in the world? Where is the f***king UN?" he asks. "This is happening every day … Where's America? … Are we animals dying here?"
In another video, also dated 8 February, Daymen stands over the lifeless body of what appear to be a small girl.
He says that the girl was killed by a mortar, and asks "is this what the UN is waiting for?"
The UN says close to 6,000 people have been killed in the country since the start of anti-government protests in March 2011.Suggest a correction