Rebels seized a U.N.-operated border crossing on the demilitarized zone linking Israel and Syria on Thursday, activists said, following heavy clashes between the opposition and President Bashar al-Assad’s forces. It is the only crossing between the two countries and it was the first time Syrian rebels had managed to take the place. However, it was unclear if they could hold it for long, with fighting still raging in the area. Israel is worried that the Golan, which it captured from Syria in 1967, will become a springboard for attacks on Israelis by jihadi fighters, who are taking part in the...