United Nations special envoy Kofi Annan has warned that the current peace plan for Syria may be the last chance to avoid civil war.
The BBC reports he told a closed session that the plan was "not an open-ended commitment" and highlighted continuing violations.
The Syrian army is now using fewer heavy arms, he said, but human rights violations appear to be intensifying.
Mr Annan told the Security Council he was particularly concerned that torture, mass arrests and other human rights violations were "intensifying".
He also told the council that Syrian President Bashar al-Assad bore "primary responsibility" for ending the military campaign.
After the briefing, he told a news conference that the ceasefire-monitoring mission was "the only remaining chance" to stabilise Syria.
"There is a profound concern that the country could otherwise descend into civil war, and the implications of that are quite frightening. We cannot allow that to happen," he said.
The peace plan brokered by Mr Annan was agreed a month ago and includes the deployment of 300 UN monitors, but it has failed to end the violence in Syria.
UN convoy targeted
An explosion hit a Syrian military truck escorting a convoy of UN observers near the city of Deraa, just seconds after the observers passed by on Wednesday.
The head of the UN team, Major-General Robert Mood was in the convoy, but neither he nor any of the other monitors was hurt.
Eyewitnesses said at least three Syrian soldiers were wounded.