GAZIANTEP, Turkey -- Syria pulled both Turkey and Israel closer to military entanglements in its civil war on Monday, bombing a rebel-held Syrian village a few yards from the Turkish border in a deadly aerial assault and provoking Israeli tank commanders in the disputed Golan Heights into blasting mobile Syrian artillery units across their own armistice line.
The escalations, which threatened once again to draw in two of Syria's most powerful neighbors, came hours after the fractious Syrian opposition announced a broad new unity pact that elicited praise from the big foreign powers backing their effort to topple President Bashar al-Assad.
"It is a big day for the Syrian opposition," wrote Joshua Landis, an expert on Syrian political history and the author of the widely followed Syria Comment blog. Mr. Landis, director of the Center for Middle East Studies at the University of Oklahoma, wrote that the "Assad regime must be worried, as it has survived for 42 years thanks to Syria's fragmentation."
There has been speculation that Mr. Assad, feeling increasingly threatened, may deliberately seek to widen the conflict that has consumed much of his own country for the past 20 months and left roughly 40,000 people dead. Although there is no indication that Mr. Assad has decided to try to lure Israel into the fight, any Israeli involvement could rally his failing support and frustrate the efforts of his Arab adversaries.
The attack on the Turkish border, by what Syrian witnesses identified as a Syrian MIG-25 warplane, demolished at least 15 buildings and killed at least 20 people in the town of Ras al-Ain, the scene of heavy fighting for days and an impromptu crossing point for thousands of Syrian refugees clambering for safety into Turkey.
"The plane appeared in seconds, dropped a bomb and killed children," said Nezir Alan, a doctor who witnessed the bombing. "Here is total chaos." In a telephone interview from Ras al-Ain, he said the bombing wounded at least 70 people, 50 of them critically. Turkish television stations reported that ambulances were rushing victims into Ceylanpinar, Turkey, just across the border.
Windows of shops and houses in Ceylanpinar were shattered by the force of the bombing, and Turkish television showed people on both sides of the border running in panic, while military vehicles raced down streets as a huge cloud of smoke hung over the area.
There were no immediate reports of deaths or injuries in Ceylanpinar. But the Turkish authorities, increasingly angered by what they view as Syrian provocations, have deployed troops and artillery units along the 550-mile border with Syria and have raised the idea of installing Patriot missile batteries that could deter Syrian military aircraft.
Turkey's foreign minister, Ahmet Davutoglu, sent a diplomatic note to Syria on Monday to protest the Ras al-Ain bombing, the semiofficial Anatolian News Agency reported.
Civilians in southern Turkey's provinces of Hatay, Sanliurfa and Gaziantep, where the government has erected camps for Syrian refugees, have been advised not to travel close to the border.
In Israel, the military said Israeli tanks that are deployed in the Golan Heights, which the Israelis seized from Syria in the 1967 war, had made a direct hit on Syrian artillery units on Monday after consecutive days of erratic mortar fire coming from the Syrian side of the armistice line. The Syrian mortar shells caused no damage or casualties, the military said.
Military officials and analysts in Israel said that they viewed the Syrian shelling as unintentional spillover from the civil war and that Israel has no desire to get involved in the Syria conflict. But the Israelis have expressed increasing concern that after four decades of relative stability in the Golan area, the Assad government may be trying to push them into a fight that could galvanize Arab hostility toward Israel and distract attention from its own problems.
If an errant Syrian shell hit a school filled with children on the Israeli side, said Prof. Moshe Maoz at the Hebrew University of Jerusalem, a strong Israeli response would be all but guaranteed. "Assad knows very well that Israel does not have a sense of humor here and can retaliate very heavily."
The United Nations, which monitors an armistice agreement between Israel and Syria in force since the 1973 war, has said it fears that Golan violence could jeopardize the cease-fire.
In Doha, Qatar, where Syrian opposition figures had been meeting since last week, the agreement reached Sunday on forming a new umbrella organization, which could become the basis for a provisional government, was welcomed by participants and the effort's foreign backers, including Turkey, the United States, the European Union and the Arab League. There were expectations that the new group, called the National Coalition of Syrian Revolutionary and Opposition Forces, would be permitted to take Syria's seat at the Arab League, which had expelled Mr. Assad's representative.
Turkey's Foreign Ministry released a statement saying that the agreement "would add momentum to efforts in completing the democratic transition process in line with the legitimate expectations of the people."
In the northern Syrian city of Aleppo, a focal point of the conflict since this summer, civilians who have been living under the threat of constant shelling by the Syrian Army welcomed the opposition unity agreement and expressed hope that it signaled a turning point.
"We have been waiting for this for a very very long time," said Abu al-Hasan, an anti-Assad activist in Aleppo who was reached by telephone. "Even if it is not perfect yet, it will save us." But he also warned that "people do not believe this will stop the shelling like a miracle."
There was no sign that the violence was abating elsewhere inside Syria. Activist groups said warplanes were dropping bombs in Damascus suburbs and that army snipers had taken up positions in areas where bombs had been dropped. The mayhem surrounding central Damascus made residents in that part of the capital feel increasingly isolated.
"The inside of the city is like a big prison now," said Alexia Jade, a media activist contacted inside Damascus. "The checkpoints have increased and the lines of cars waiting to be searched are getting longer."
Sebnem Arsu reported from Gaziantep, Turkey, and Rick Gladstone from New York. Reporting was contributed by Isabel Kershner and Jodi Rudoren from Jerusalem, and Hania Mourtada from Beirut, Lebanon.
This article originally appeared in The New York Times.