Raging battles between the Syrian troops, backed by pro-regime militias, and the opposition forces in several parts of country claimed at least 50 lives on both sides in the last 24 hours.
The Syrian opposition forces attacked military camps in the northwestern governorate of Idlib and killed at least 15 soldiers, The Syrian Observatory for Human Rights (SOHR) reported on Sunday.
The attack, jointly launched by Al-Nusra Front (NF) and other Islamist militant groups, targeted Wadi Al-Dhaif and Al-Hamediya camps.
At least eight attackers were also killed in the battles which are still going on.
The NF fighters claimed control over the security checkpoints of Al-Ra'ei, A-Dhab'an and Al-Za'lana in Wadi Al-Dhaif and Al-Hamediya military camp in Ma'aret Al-No'man city.
They used US-made TOW anti-tank missiles to destroy several military vehicles, according to the report.
Meanwhile, the regular troops, backed by local and foreign pro-regime militias including the Lebanese Hezbollah and the Palestinian Al-Quds Brigade, attacked the opposition forces in Mazare' Al-Mallah and Handarat towns on the northern rural outskirts of Aleppo city.
They managed to kill 21 opposition fighters and control the eastern part of the town while Al-Quds Brigade suffered one fatality.
The regular troops try to advance on the western part in a bid to cut off the supply lines of the opposition stronghold in Aleppo, SOHR added.
However, the Shaam News Network cited opposition sources as claiming that they managed to repel a major offensive by the regular troops and inflicted heavy human and material damage on the attackers.
Refuting the regime's claims of victories in the fiercest attack by the regular troops in the area, the opposition fighters said they killed a large number of soldiers, captured four others, and destroyed a launch bad of the Russian-made anti-tank Metis missiles and an armored vehicle of ZSU-23-4 Shilka type.
In Damascus governorate the raging battles between Jaish Al-Islam and Jaish Aswad Al-Sharqia, on one hand, and the Islamic State in Iraq and the Levant, on the other, claimed 13 lives on both sides in the last 24 hours.