Nine people including Syrian military personnel were killed and 100 wounded today in bomb blasts near security service buildings in Idlib, state media said.
Rights activists claim more than 20 people were killed as a bombing campaign intensified against government targets.
Twin explosions, the latest to disrupt a shaky UN truce, blew fronts off nearby buildings and left craters in roads, according to images on state television that showed people at the scene condemning the rebels who are fighting to oust President Bashar al-Assad.
State television blamed both blasts in the restive northwestern city on suicide bombers.
A prominent human rights activist said they appeared to target local headquarters of intelligence services for the air force and the army, two of the many security agencies that have helped keep the Assad family in power for four decades.
The activist, at the British-based Syrian Observatory of Human Rights, put the death toll at over 20. He also reported
casualties from a third blast in Idlib several hours later, although he gave no further details.
State media said monitors from the United Nations team sent in to oversee the 18-day-old ceasefire were visiting the scene in Idlib. Foreign Ministry spokesman Jihad Makdissi said the head of the monitoring mission, Norwegian general Robert Mood, was being briefed on "violations by armed opposition".
Meanwhile, Syrian soldiers fired at a group of one Swiss and three Lebanese skiers along the mountainous border today, wounding one, after they mistook them for smugglers, Lebanese security sources said.
The group of four were skiing on Mount Herman in Lebanon's east when one of the Lebanese men, Antoine Hajj, was shot in the shoulder, they said.
"Once they came under fire from the Syrian army post, the skiers started screaming to them to hold fire," the security
source said on condition of anonymity as he was not authorised to speak to the press.
The Syrian border guards then entered Lebanon, he said, and told the skiers that they could leave. They then walked for four hours to the nearest Lebanese security post, he added.
The Syrian army has at times entered Lebanon briefly and opened fire on people they suspect of smuggling weapons into Syria across the poorly demarcated border.
The United Nations says security forces have killed 9,000 people in the uprising, which started as peaceful mass protests inspired by rebellions elsewhere in the Arab world but which is becoming an increasingly bloody guerrilla insurgency.
Damascus says 2,600 from its forces have died at rebel hands and has accused the United Nations of turning a blind eye to "terrorist acts" committed by those fighting for the removal of Dr Assad, who succeeded his late father, Hafez al-Assad, in 2000.
Although the rebels are far from a unitary force, their tactics appear to be shifting from small-scale ambushes on checkpoints and military patrols to assaults on infrastructure and symbols of the Assad state.
"We are starting to get smarter about tactics and use bombs because people are too poor and we don't have enough rifles. It is just no match for the army. So we are trying to focus on the ways we can fight," said one anti-Assad fighter who claimed to be in command of a militia unit.
Gen Mood acknowledged the huge task awaiting the planned 300-strong unarmed mission, which now has 30 people on the ground, but said he was confident it could make headway.
"We will be only 300, but we can make a difference," Gen. Mood told reporters on his arrival in the Syrian capital."Thirty unarmed observers, 300 unarmed observers, even 1,000 unarmed observers cannot solve all the problems," he said.
"I call on everyone to help us and cooperate with us in this very challenging task ahead."
The United Nations says President Bashar al-Assad's forces have killed 9,000 people during the revolt, the latest in a string of uprisings in the Arab world against autocratic rule. Damascus says 2,600 of its personnel have died at the hands of anti-Assad militamen, and has accused the United Nations of turning a blind eye to "terrorist acts" against security forces.
Both sides have been accused of multiple violations of the ceasefire engineered by UN-Arab League envoy Kofi Annan. Under the deal, Dr Assad's tanks and troops are supposed to return to barracks. Damascus says this has happened, although UN secretary general Ban Ki-moon disagreed this week, saying he was "gravely alarmed by reports of continued violence."
Reuters