Syrian soldiers fought rebels Tuesday in a firefight that killed nine people and sent several mortars sailing across the border into the Israeli-occupied Golan Heights.
The Israeli military said nobody was hurt in the shelling and that the spillover was believed to be accidental. But Israel filed a complaint to the United Nations peacekeeping force that patrols the tense region between Israel and Syria.
Over the course of the 18-month-old uprising against Syrian President Bashar Assad, violence has spilled into neighboring Lebanon, Jordan and Turkey. In July, mortar shells fell about one kilometer (half a mile) from the Golan boundary.
The spillover is among the most worrying developments from the Syria crisis, which has the potential to enflame the entire region.
Activists said Tuesday that the clashes between troops and rebels inside Syria killed at least nine people.
On Tuesday, United Nations Secretary-General Ban Ki-moon demanded international action to stop the war in Syria, telling a somber gathering of world leaders that the 18-month conflict had become "a regional calamity with global ramifications."
"The international community should not look the other way as violence spirals out of control," Ban said.
Also at the United Nations, Secretary of State Hillary Rodham Clinton and the U.N.'s new Syria mediator Lakhdar Brahimi discussed ways to unite Syria's opposition and advance a political transition.
A senior U.S. official said the two discussed new strategies for dealing with the Assad regime. The official demanded anonymity because he was not authorized to speak publicly on the matter.
An Israeli defense official said the military believes Tuesday's incident in the Golan Heights was a mistake and the mortars were not aimed at the Jewish state. It was not the first time shells from Syria exploded in Israel since the uprising began, the official said on condition of anonymity because he is not allowed to brief the media.
There have been concerns in Israel that the long-quiet Israel-Syria frontier area could become a new Islamist front against the Jewish state. Israel captured the Golan Heights from Syria in the 1967 Mideast war and annexed the plateau 14 years later.
Syria and Israel are bitter enemies and have fought several wars, including the 1973 war. Despite the animosity, the border with Syria has been Israel's quietest since then.
The defense official said Israel is concerned that the border region could become as lawless and deadly as Israel's frontier with Egypt's Sinai Peninsula has become since the fall of longtime Egyptian President Hosni Mubarak last year.
The Israeli news site YNet quoted a resident near the border as saying the mortars struck an area filled with apple trees.
"All in all there has been a lot shooting and mortars really close to the border," Dudi Mored, resident of Kibbutz Elrom, an Israeli settlement in the Golan, told Ynet.
Although the uprising against Assad has been an unprecedented challenge to his family's four-decade ruling dynasty, the regime has managed to keep its grip on power. Neither side of the conflict has been able to deal a decisive blow, leading to a grinding and deadly stalemate. Activists estimate that the conflict has killed some 30,000 people since the revolt began in March 2011.
On Tuesday, several bombs went off inside a school in the Syrian capital that activists say was being used by regime forces as a security headquarters. Ambulances rushed to the area and an initial report on state media said seven people were wounded.
An amateur video posted online showed smoke billowing from several spots in an area near a major road. The narrator said: "A series of explosions shake the capital Damascus." The authenticity of the video could not be independently confirmed.
Over the past few months, rebels have increasingly targeted security sites and symbols of regime power, particularly in the main cities of Damascus and Aleppo, in a bid to turn the tide.
In July, a bombing in the heart of Damascus killed four senior security officials including the defense minister and Assad's brother-in-law. Other large blasts have targeted the headquarters of security agencies in the capital, killing scores of people this year.
Abu Hisham al-Shami, an activist based in Damascus, told The Associated Press via Skype that the "Sons of Martyrs School" had recently been turned into a regime security center. He said government forces use the school as a base to fire mortars at rebellious neighborhoods.
State-run television quoted the director of the school, Mohammed Amin Othman, as saying that two bombs exploded inside the school, wounding seven people and causing minor damage. State TV said the bombs were planted by "terrorists," the term the government uses for rebels.
Othman said in a statement carried by the official SANA news agency that no students were at the school at the time of the blast because it does not open until next week. Although the school year started last week in Syria, Othman said the boarding school opens later.
The Britain-based Syrian Observatory for Human Rights said 20 people were wounded, some of them seriously, in several blasts at the school. It said most of the wounded were members of the military.
A worker outside the school, who refused to be identified, said two diesel tankers exploded inside the school compound, wounding at least four people, one of them seriously. He added that the wounded were rushed to nearby hospitals.
He said a thick plume of smoke billowed over the area and fire reached the fifth story of the building. A nearby theater for the school's students was partially damaged and the blast caused its ceiling to collapse.
Also Tuesday, Syrian rebels released Lebanese citizen Awad Ibrahim, who was one of 11 Shiite Muslim pilgrims abducted in May shortly after entering Syria from Turkey on their way to Lebanon, the Lebanese state-run National News Agency reported.
Ibrahim, who crossed into Turkey Tuesday afternoon and expected to fly home later, is the second to be released. The nine others are still being held in northern Syria.
His release came after two Turkish citizens and several Syrians were set free in Beirut after being abducted by Lebanese tribesmen to press for the release of Lebanese. Turkey hosts leading Syrian opposition figures and rebel commanders.
In Jordan, dozens of Syrian refugees angry over harsh living conditions in their desert tent camp clashed with Jordanian police, hurling stones and smashing charity offices and a hospital, officials and refugees said Tuesday.
The rioting late Monday in the Zaatari camp was the worst violence since the facility opened in July near the Jordan-Syria border. More than 25 policemen were injured by stones thrown by the refugees, a police official said.
A Syrian refugee in the camp, Abu Nawras, said police fired tear gas to disperse the protesters who were demanding improved conditions, better food and education for their children.
The camp, which hosts about 32,000 Syrians who fled the civil war at home, has seen smaller protests in the past weeks as refugees mostly complained about snakes and scorpions, and demanded their tents be replaced with trailers so they can better protect themselves from the scorching sun, cold nights and ubiquitous dust.
Hundreds of thousands have fled the chaos in Syria as the uprising against President Bashar Assad turned increasingly violent. Jordan alone has taken in some 200,000 Syrians — the largest number in the region — while Turkey, Lebanon and Iraq have taken in the rest.
Associated Press writers Daniel Estrin and Ian Deitch in Jerusalem, Jamal Halaby in Amman, Jordan, and Bradley Klapper in New York contributed to this report.