* Syria mediator has proposed Eid al-Adha ceasefire
* UN Security Council needs to approve peacekeepers
The United Nations is preparing various contingency plans to send peacekeepers to Syria as part of a ceasefire or political deal, but it is too early say how many would be needed, U.N. peacekeeping chief Herve Ladsous said on Monday.
The U.N.-Arab League mediator in the Syria conflict, Lakhdar Brahimi, is attempting to persuade the Syrian government and rebels to accept a ceasefire during the three-day Islamic holiday of Eid al-Adha that starts on Friday.
If there were a more sustained ceasefire, the U.N. Department of Peacekeeping Operations has told Brahimi it could put together a force of up to 3,000 monitors to keep fighters separated and maintain the truce, diplomats said.
"I would confirm that, of course, we are giving a lot of thought to what would happen if and when a political solution or at least a ceasefire would emerge," Ladsous, the U.N. under-secretary-general for peacekeeping operations, told reporters.
"There are a number of hypotheses, but I think at this stage one can only say that it certainly would be premature to mention a figure because it would depend on the situation and on the tasks," he said.
Brahimi's suggested Eid al-Adha truce would be self-imposed, with no monitoring. Sending any U.N. monitors to Syria would require a U.N. Security Council mandate.
But Syrian rebels cast doubt on Monday on prospects for a temporary truce, saying it was not clear how an informal ceasefire this week could be implemented.
Neither Syria's army nor the rebels have shown signs of easing off as Eid nears. More than 200 people were killed on Sunday in fighting and bombardments, including 60 soldiers, the Syrian Observatory for Human Rights said.
Brahimi, who took over from Kofi Annan after the former U.N. secretary-general resigned in frustration in August, has been traveling in the Middle East urging key regional powers to use their influence.
Brahimi said last week that a respite in hostilities could build confidence and help bring about a longer truce in the 19-month-old conflict. A previous ceasefire in April collapsed after just a few days, with each side blaming the other.
"Right now the focus is really on Lakhdar Brahimi's efforts to achieve a ceasefire whether temporary or more durable," Ladsous said. "It's a shocking fact that everyday 150 to 200 civilians are killed and it has almost become part of the background noise and it is simply unacceptable."
"Depending on changes on the ground and on the decision by the Security Council we stand ready to assist further," he said.
Under Annan's failed truce, some 300 monitors and around 100 civilian experts began deploying to Syria in April to oversee a ceasefire that was never realized. As the conflict worsened, the Security Council allowed the force's mandate to lapse and the unarmed monitoring team withdrew in August.