The Arab League delegation arrives a day after what activists called the bloodiest in the nine-month crackdown on protests against the rule of Bashar al-Assad.
The Syrian Observatory for Human Rights said Syrian forces killed 111 civilians and activists on December 19. It said another 100 soldiers were either killed or wounded.
In a stement, Turkey's Foreign Ministry accused Assad's regime of turning Syria into a "bloodbath" by continuing attacks against civilians.
France branded the killings an "unprecedented massacre" and the United States said Syrian authorities had "flagrantly violated their commitment to end violence."
Washington again called on Assad to step down.
Activists say more than 200 civilians have been killed in Syria over the past 48 hours.
The Syrian National Council called for "safe zones" to be set up under international protection and that they be declared 'disaster areas' to allow for humanitarian aid.
Damascus signed a protocol to allow the Arab monitors on December 19 after weeks of foot dragging.
The monitors are tasked with making sure Syria is fulfilling the Arab League plan to end the violence, including a withdrawal of troops from towns and cities, a release of prisoners and a dialogue with the opposition.
Damascus claims more than 1,000 prisoners have been freed since the plan was agreed six weeks ago and that the army has pulled out of cities.
compiled from agency reports