Clashes erupted between regime forces and rebels in Syria's Idlib province overnight, killing two opposition fighters, as two others died in the Damascus region on Monday, a watchdog said.
The rebels were killed in Kafr Nabal town of Idlib province in the northwest of the country, the Syrian Observatory for Human Rights said.
The Britain-based watchdog said several explosions were also heard in the Jabal al-Zawiya region of Idlib.
The main opposition Syrian National Council reported violence across Idlib, saying regime forces were using "tanks, rocket launchers and artillery" to bombard several parts of the province, a rebel stronghold neighbouring Turkey.
The towns targeted included Kafr Nabal, Jabal al-Zawiya, Maaret al-Numan, Ariha and Ramah, the SNC said.
In the capital, regime forces stormed the Jubar neighbourhood following an Internet outage in the area, the Observatory said, adding that a man was killed in a raid on the Qaboon district.
It said regime forces shot dead a young man in Douma, 10 kilometres (six miles) from Damascus.
The Observatory earlier said four explosions rocked the town of Irbin in Damascus province and smoke could be seen rising from a military checkpoint between Irbin and Qaboon.
Violence in Syria has continued unabated with 46 people killed across the country on Sunday, including 19 civilians, 19 soldiers and 8 rebels.
The Observatory says as many as 2,400 of the more than 13,500 people killed in an anti-regime uprising have died since a putative UN-backed ceasefire began on April 12. Days later unarmed UN observers began deploying in Syria.
The 15-month unrest has spilled over into Lebanon, with clashes between pro- and anti-Syrian regime gunmen in the northern city of Tripoli leaving 14 people dead over the weekend, a Lebanese security official said.