At least 30 people - including 23 soldiers - have died in heavy overnight clashes in the central Syrian city of Rastan.
The Syrian Observatory for Human Rights said dozens of others were wounded in the city while three troop carriers were destroyed in fighting.
If confirmed, the attack would be one of the deadliest suffered by security forces in the 14-month-long uprising against President Bashar al-Assad.
It comes after government forces launched a fresh assault on Rastan during the weekend, despite a UN-backed nominal ceasefire that was supposed to come into effect just over a month ago.
Meanwhile, the EU has imposed another round of sanctions on Syria - the 15th so far - in an effort to increase pressure on the government.