The Syrian troops clashed with the rebels in the Turkey border on Friday, the first sign of violation of the UN backed ceasefire.
The clashes took place in the north-western village Khirbel el-Joz bordering Turkey, the Associated Press reported quoting the Syrian Observatory for Human Rights based in Britain.
No major rocket attacks or shelling occurred though the clashes indicated violation of the cease fire deal brokered by UN special envoy, Kofi Annan.
The incident occurred even as a 30-member UN-sponsored peace team is about to visit Syria to observe the ceasefire progress.
The latest clashes indicate the fragility of the ceasefire which was holding well initially.
Meanwhile, the opposition activists called for a mass protest to put the ceasefire on test on Friday.
"Tomorrow, like every Friday, the Syrian people are called to demonstrate even more and put the regime in front of its responsibilities - put the international community in front of its responsibilities," the AP has quoted the leader of the opposition Syrian National Council, Burhan Ghalioun as saying.
The opposition protests are expected to aggravate the mutual distrust surrounding the ceasefire. At the same time, it is feared that the protest might trigger fresh violence.
Though the regime stopped its major attacks from Thursday morning, the situation remained unstable with few violent incidents reported around the place.
The international community is constantly keeping a skeptic eye on the Syrian state of affairs even after its promise, since the regime's track record was not reliable.
"The onus is on the government of Syria to prove that their words will be matched by their deeds at this time," the AP quoted the UN Secretary General Ban Ki-Moon as saying in an earlier occasion.
"This ceasefire process is very fragile. It may be broken any time," he added.
The UN Chief also admitted that it is difficult to assess the situation on the ground in the absence of UN observers hence assured that the team will be sent as promptly as possible.
The hard-won ceasefire on Thursday has briefly stopped the year-long violence which so far claimed more than 10,000 lives.