(CNN) -- Dozens of Syrians were slaughtered by regime forces in early morning violence Tuesday, opposition activists said, despite the growing presence of U.N. monitors in the country.
By 8 a.m., at least 25 people were killed, including an entire family and defected soldiers, said the Local Coordination Committees of Syria, a network of opposition activists. Seventeen people died "in a massacre committed by the regime forces in Idlib towns," the LCC said.
The latest reports of bloodshed came just hours after some opposition activists said the deployment of U.N. monitors on the ground have helped stymie the violence somewhat, but not enough to bring the government into compliance with a U.N.-backed peace plan that the Syrian regime had accepted.
"Shelling has calmed, but this does not mean that the peace plan has been implemented," said an activist in Homs identified only as Saleem for safety reasons. "Gunfire, rocket shelling, mortar shelling and arbitrary arrests still occur."
And in Hama, an LCC member named Mousab said the situation in his city is "more quiet," but added that civilians are not able to talk to U.N. observers because they are always flanked by government forces.
But Ahmad, another opposition activist in the northwestern Idlib province, said the observers' presence may stifle violence in the short-term, but the situation can change quickly after they depart.
"Unfortunately, the monitors are like a guide for the Syrian regime: Wherever they go, usually people are killed after they leave," Ahmad said Monday night.
U.N. Under-Secretary-General for Peacekeeping Operations Herve Ladsous is expected to brief the media Tuesday on the observer mission in Syria.
The "massacre" in Idlib province towns Tuesday followed reports of two car bomb explosions in the city of Idlib on Monday.
The blasts left at least 20 people dead, said the opposition Syrian Observatory for Human Rights. The state-run Syrian Arab News Agency (SANA), meanwhile, reported eight civilian and law enforcement members were killed.
Photos posted on SANA's website showed buildings in ruins, cars crushed by debris and the bloody remains of victims.
State media reported that about 100 people -- mostly civilians -- were injured in the explosions. Citing medical sources, the observatory said the dead were mostly security force members. One car bomb targeted a government security building, the LCC said.
A video posted on the rebel Free Syrian Army's Facebook page purportedly shows FSA commander Afif Suleiman denying that the rebel army was involved in the Idlib blasts on Monday.
"We deny any involvement in the attacks ... and we would like to state that we are still committed to the cease-fire since it was announced on 4/12/2012 in halting all military operations in respect to Kofi Annan's peace plan," the video states. "And we hold the Syrian regime fully responsible for these blasts because it is in the regime's best interest to stage these attacks so they don't have to move the tanks and the heavy weaponry from the cities in their continuous crackdown against the innocent civilians in their pursuit of freedom and dignity."
CNN cannot independently the authenticity of the video, nor can it verify reports of violence and deaths within Syria, as the government has restricted access by most of the international media.
Syria has been engulfed in violence since March 2011, when government forces started cracking down on demonstrators who were peacefully protesting al-Assad's regime. The president's family has ruled Syria for 42 years. Some opposition members, including a number of military defectors, have since taken up arms against the regime forces.
The United Nations estimates that at least 9,000 people have died in the conflict, while opposition groups put the death toll at more than 11,000.
Both the Syrian regime and the rebel Free Syrian Army have accepted a peace plan laid out by Annan, the U.N.-Arab League special envoy. A key element of the plan involves a cease-fire by all parties, plus the withdrawal of Syrian forces from populated areas.
Another component is the presence of unarmed U.N. military observers. About 30 of them were on the ground Monday, and a total of 50 are expected by Friday, said Annan spokesman Ahmad Fawzi via Twitter. The U.N. Security Council has authorized up to 300 monitors in Syria.
"This is a matter of utmost urgency for the United Nations, and all efforts are in place to make sure that we get the people on the ground as quickly as possible," Neeraj Singh, the observer team's spokesman, said Sunday.
Since the cease-fire deadline passed April 12, more than 700 people have been killed, the LCC said.
The U.N. monitoring mission's leader, Maj. Gen. Robert Mood of Norway, conceded that his group's efforts are futile unless all sides commit to peace.
"Ten unarmed observers, 30 unarmed observers, 300 unarmed observers, even 1,000 unarmed observers cannot solve all the problems," Mood told reporters on Sunday. "So I call on everyone to help us and cooperate with us in this very challenging task ahead of us."