srael is crossing Tehran's red lines, and the situation is becoming serious, a senior adviser to Iran's Supreme Leader said on Friday, after Israel attacked Tehran-backed Hezbollah's central headquarters in Beirut's southern suburbs.

A senior Israeli official told reporters that Hezbollah leader Sayyed Hassan Nasrallah was the target of the strike.

"The assassinations will not solve Israel's problem. ... With the assassination of resistance leaders, others will take their place," Ali Larijani told Iran's state TV.

A senior Iranian security official told Reuters earlier that Tehran is checking the status of Nasrallah. A source close to Hezbollah told Reuters that Nasrallah was alive.

Iran's President Masoud Pezeshkian condemned the attack as a "clear and undeniable war crime that revealed once again the nature of state terrorism of the Zionist regime (Israel)," Iranian state media reported.