The UN Security Council voted unanimously in favour of adopting a Russia-European resolution authorises the deployment of up to 300 unarmed military observers to Syria, to be known as UNSMIS.
The move comes less than day after UN ceasefire monitors entered the city of Homs.
Stating that the violence between government forces and opposition activists was "clearly incomplete", the resolution warned that "further steps" may be necessary if the agreement is not adhered to.
The resolution stipulated that the deployment would depend on the Assad regime's compliance with the UN Secretary General's six point peace plan.
The US ambassador to the UN, Susan Rice, said,
"The United Nations Security Council has called upon the government to take concrete actions,"
"The Syrian government has ignored this council. In the United States, our patience is exhausted."
"We will not wait 90 days to pursue measures against the Syrian government if it continues to violate its commitments or obstruct the monitors' work."