JERUSALEM — Four rockets fired from Syrian territory landed in the Israeli-held part of the Golan Heights and in Israel’s Upper Galilee on Thursday, prompting Israeli retaliatory strikes against more than a dozen Syrian posts, according to the Israeli military.

Israel blamed Iran for what appeared to be the most serious flare-up in the area in months.

There were no casualties on the Israeli side, but the rocket attack comes at a diplomatically delicate time as Israel tries to lobby the United States Congress to reject what Israel views as a detrimental nuclear deal reached between the world powers and Iran.

An Israeli military official said the rocket fire was “clearly intentional,” as opposed to errant rockets and mortar shells that have landed in Israeli-held territory as a result of spillover from the Syrian civil war. The official, who spoke on the condition of anonymity in line with army rules, said it was probably the largest salvo of rockets fired out of Syria toward Israel in four years.

The Israeli news media said this was also the first time that rockets launched from Syrian territory had landed in the Galilee since the 1973 war.