EU member states want Russia to put pressure on its ally to withdraw heavy weapons from cities and comply fully with UN envoy Kofi Annan's peace plan.
Russia and China are also resisting US and European calls to condemn President Bashar al-Assad and seek his removal.
On Sunday, Mr Assad denied his forces had any role in the Houla massacre.
In a televised address, President Assad told parliament the killing of more than 108 people in their homes, including 49 children, was an "ugly crime" that even "monsters" would not carry out.
Witnesses have blamed pro-government militiamen for the massacre, which has triggered international condemnation and led to several countries expelling Syrian diplomats in protest.