The Syrian Observatory for Human Rights, which covers the opposition movement against President Bashar al-Assad's regime, says a rebel ambush in northern Syria has killed 15 government forces.
The group claimed the troops, including two colonels, were killed May 2 in the northern province of Aleppo.
It said two rebels were killed.
The report could not be independently confirmed.
The report comes a day after opposition fighters claimed they killed at least 12 government troops in the eastern province of Deir al-Zor and at least 10 people died in a mortar attack in Syria's northern Idlib Province.
On April 30, multiple blasts in Idlib left at least 20 people dead.
The fighting comes as a team of United Nations monitors is in Syria, attempting to uphold an internationally backed cease-fire. The UN says it is aiming to deploy all 300 monitors approved by the Security Council by the end of May.
UN Under-Secretary-General for Peacekeeping Operations Herve Ladsous told reporters on May 1 that there are currently 24 peacekeepers on the ground, and about 150 observers committed to the mission thus far.
The observers are monitoring a shaky cease-fire which has been in place since April 12.
Ladsous said the observers are reporting violations of the cease-fire by both President Bashar Al-Assad's security forces and opposition groups.
The monitors have been criticized for staying indoors on Fridays, when mass demonstrations have traditionally taken place during the 14-month-long uprising.
Ladsous said the observers are working days and some nights in an effort to help put an end to violence.
Based on reporting by Reuters, AFP, and RFE/RL