"A decision has been taken to stop these missions as of the morning of Thursday, April 12, 2012," the statement said, adding: "Our armed forces are ready to repulse any aggression carried out by the armed terrorist groups against civilians or troops."
The government denies that it is facing an uprising by Syrians who want to dislodge the authoritarian family dynasty that has ruled the country for more than four decades. Instead, the regime says, terrorists are carrying out a foreign conspiracy to destroy Syria.
Because the regime has treated any sign of dissent as a provocation, there are only dim hopes for an abrupt end to the bloodshed.
The White House cautioned that President Bashar al-Assad's regime has reneged on promises to stop the violence in the past.
"What is important to remember is that we judge the Assad's regime by its actions and not by their promises, because their promises have proven so frequently in the past to be empty," White House spokesman Jay Carney told reporters in Washington.
Annan is to brief the U.N. Security Council on Thursday by videoconference from Geneva.
The rebel Free Syrian Army, a fighting force determined to bring down Assad, has said it will abide by the cease-fire Thursday. But the opposition is not well organized, and there are growing fears that there are groups looking to exploit the chaos.