In a statement Saturday, major general Robert Mood, head of the UN mission to Syria, halted operations “until further notice”.
It comes amid claim that Syrian government forces has recommenced shelling in the capital Damascus, killing 12 people, according to opposition figures.
The past two weeks have seen a worrying escalation in violence in the country. A massacre in the town of Houla on May 25 resulted in the deaths of more than 100 people, many of them women and children.
That attack resulted in a series of stern warnings against the regime of President Bashar al-Assad and renewed calls for his removal from power.