Israel and Iran traded fire on Monday, seriously testing a fragile truce and threatening hopes for a deal to end the Middle East war.

The new attacks, including a strike on an Iranian petrochemical complex, came hours after U.S. President Donald Trump called on Israel to refrain from retaliating against Tehran's missiles.

U.S. President Donald Trump said Sunday he will call Israeli Prime Minister Benjamin Netanyahu to urge him not to retaliate against Iranian missile strikes on Israel, U.S. news outlet Axios reported.

"I am going to call Bibi right now and tell him not to retaliate," Trump was quoted as saying by Axios journalist Barak Ravid in a phone interview, using the Israeli leader's nickname.

Air raid sirens sounded in Israel on Sunday as its military worked to intercept barrages of incoming Iranian missiles for the first time since an April ceasefire took hold in the Middle East war.

The Israeli army reported the attack just hours after Tehran had threatened to retaliate for a new Israeli strike on Beirut's southern suburbs.

The Israeli military said Sunday it uncovered a sprawling tunnel network beneath the Beaufort castle in southern Lebanon, saying it was built to give Hezbollah a fortified strike hub just kilometers from Israeli territory.

Israeli soldiers recaptured the crusader-era castle recently, giving the military a strategic toehold it once occupied for nearly two decades.

Iran threatened to retaliate against the United States and Israel for fresh strikes in Beirut's southern suburbs on Sunday, further dampening hopes for a lasting peace as the Middle East war reached its 100th day.

U.S. President Donald Trump called for "more surgical" strikes against Hezbollah in Lebanon and said he is not demanding the conflict be included in a peace deal with Iran, in an interview broadcast Sunday.

"I'd like to see a more surgical attack on Hezbollah. I think it should be more surgical," Trump told NBC's "Meet the Press," according to a transcript of the interview recorded Friday.

Israel's military struck alleged Hezbollah command centers in Beirut's southern suburbs in response to rocket fire on northern Israel, Prime Minister Benjamin Netanyahu's office said Sunday.

"In accordance with the directives of Prime Minister Netanyahu and Defense Minister Katz, the Israel Defense Forces have just struck a militant command center in Beirut's Dahiyeh district, in response to Hezbollah's fire towards Israeli territory," his office said.

Israel's military said Sunday that it had intercepted two projectiles launched from Lebanon into Israeli territory, despite a new ceasefire agreement announced this week aimed at ending hostilities between Israel and Hezbollah.

An Israeli strike on southern Lebanon killed two women and wounded 22 people on Saturday, Lebanon's health ministry said, despite a ceasefire in the Israel-Hezbollah war.

The Israeli army announced on Saturday the deaths of two soldiers who had been fighting in southern Lebanon, where Israel is pursuing a campaign against Hezbollah.