"The Israelis committed a historic mistake... and put themselves in direct combat with Iran," Hassan Nasrallah warned in a televised address.
Seven Iranian personnel were killed in Monday's early-morning strike on the T-4 air base in Syria, but Tehran had not specified which units the fighters belonged to.
On Friday, Nasrallah said the casualties were elite Iranian Revolutionary Guards, the first to be targeted by Israel in Syria's long-running conflict.
"This is unprecedented in seven years: that Israel directly targets Iran's Revolutionary Guard," Nasrallah said.
"This is a turning point for the region, and what came before is not what will come after," he warned.
The Observatory said a total of 14 fighters, including Iranians, died in the strike.
Moscow has said no Russians were killed in the attack.
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