Israel has portrayed the capture of a Crusader-era fortress as a turning point in its offensive against Hezbollah, but the operation has also sparked fears of a new quagmire in south Lebanon.

The capture of the castle marks a major gain for Israel since the latest Israel-Hezbollah war began in early March.

Israel has captured the 12th-century Beaufort castle that overlooks southern Lebanon and northern Israel. The move suggests Israel is planning an extended military presence in…