Israeli warplanes unleashed a series of airstrikes on Syrian military posts early Wednesday, killing one soldier and wounding seven in one of the most serious clashes between the countries in the past four decades.

The airstrikes came in retaliation for a roadside bombing a day earlier in the Golan Heights that wounded four Israeli soldiers on patrol along the tense frontier with Syria. The overnight raids marked a sharp escalation of activity for Israel, which largely has stayed on the sidelines during Syrian President Bashar Assad’s battle against rebels trying to topple him.

It is unclear which of the many groups fighting in Syria may have planted Tuesday’s bomb. But Israel has said it holds Assad responsible for any attacks emanating from his country, and accused his forces of allowing the attack to take place. […]