"Opposition leaders said Mr Yanukovych agreed to postpone a...

"Opposition leaders said Mr Yanukovych agreed to postpone a planned assault on the opposition encampment in Kiev’s Independence Square after a meeting where they struck a deal on a last-minute ceasefire."

http://www.telegraph.co.uk/news/worldnews/europe/ukraine/10650325/Ukraine-President-agrees-truce-with-opponents-as-West-prepares-sanctions.html

IMO there are two reasons these people have called a ceasefire:

a. The new head of the Army has refused to kill any more citizens, and
b. The U.S. President has told them he will sanction their personal accounts.

IMO its because these politicians have lost control of the Armed Forces.