Bombs planted by rebels have exploded at a school building occupied by security forces and pro-government militias in Damascus, in yet another strike near the centre of President Bashar al-Assad's power.
The school's director told state television that seven people were wounded in Tuesday's attack in a southeastern district of the Syrian capital.
"At exactly 9:35am, seven improvised devices were set off in two explosions to target a school used for weekly planning meetings between shabbiha militia and security officers," said Abu Moaz, a leader of Ansar al-Islam, one of the rebel groups.
Residents and activists said smoke could be seen rising from the site and that ambulances were rushing to the scene.
They suspected the attack had targeted high-ranking military officers.
A similar assassination attempt in July killed Assad's defence minister and brother-in-law.
While the 18-month conflict continued in Damascus, it also spilled over the border into Israeli territory for the first time.
Israel's military said Syrian forces fired mortar shells at villages suspected to be occupied by rebels but accidentally hit Israeli-held land in the disputed Golan Heights, causing no injuries or damage.
A spokesman said the Israeli military filed a complaint with UN forces responsible for monitoring the border area and that "fire from Syria leaking into Israel will not be accepted".
A source in the area told the Reuters news agency that the orchard where the shells fell belonged to an Israeli agricultural community which lies close to Syrian villages where fighting has flared between Syrian rebels and forces loyal to Assad.
The incidents came as the UN convened for its annual General Assembly in New York City, where Lakhdar Brahimi, the new UN-Arab League envoy, briefed the Security Council and reportedly told representatives that Assad was "not serious about making reforms".
Planted by 'terrorists'
The Damascus bombings targeted the Sons of Martyrs School, which reportedly had been turned into a military base used to fire mortars at rebellious neighbourhoods.
State-run television quoted the director of the school as saying that two bombs exploded inside, wounding seven people and causing minor damage.
The channel said the bombs were planted by "terrorists", a term that the government uses for rebels. But a governmental official told the Associated Press news agency that three people were wounded.
In-depth coverage of escalating violence across Syria
"At exactly 9:35am, seven improvised devices were set off in two explosions to target a school used for weekly planning meetings between shabbiha militia and security officers," Abu Moaz, a leader of the Ansar al-Islam rebel group, said.
"There were several officers present, and we are hoping they will be part of a large number of killed in this operation," he said.
Southern Damascus has, in recent months, become a battleground between Assad's forces and opposition fighters, turning what was thought to be Assad's untouchable seat of power into disputed territory.
Damascus residents also reported heavy clashes for two hours on Baghdad Street in a central district just to the north of the Old City.
Growing food crisis
As the weather in Syria grows colder, food will become scarcer and proper shelter more important for Syria's millions of internally displaced people.
Envoys said Brahimi told the Security Council that the country faces a growing food crisis.
He also told the 15-nation Security Council that the Syrian government estimates there are 5,000 foreign fighters in the country and is increasingly portraying the conflict as a "foreign conspiracy," delegates at the closed meeting said.
According to a diplomat in the room, Brahimi gave a very downbeat assessment of the situation, saying that the situation has gone from bad to worse.
It is the first time Brahimi has briefed the Security Council since he took the job a month ago.
He told the council that the torture of detainees has become "routine" and that people were now afraid to go to hospitals which were in the hands of government forces.
Children 'badly traumatised'
In another development, a global children's aid agency warned that Syrian children are being "badly traumatised" after witnessing killings, torture and other atrocities in their country's brutal conflict.
Save the Children said it has collected "shocking testimony" revealing that "children have been the targets of brutal attacks, seen the deaths of parents, siblings and other children, and have witnessed and experienced torture."
Released on Tuesday, the collection of first-hand accounts of the conflict from Syrian children and parents after fleeing their country contains graphic details of how children have been caught up in Syria's war, "witnessing massacres and in some cases, experiencing torture".
The report gave detailed accounts of several children who witnessed horrific atrocities in their country.
"Dead bodies along with injured people were scattered all over the ground. I found body parts all over each other. Dogs were eating the dead bodies for two days after the massacre," it quoted 14-year-old Hassan as saying.
Another Syrian boy, Wael, 16, said he knew a six-year-old boy who "was tortured more than anyone else ... he only survived for three days and then he simply died."
The global organisation urged the UN to step up its documentation of all violations of children's rights in Syria.