U.S. President Donald Trump said Monday the United States has studied a proposal for a 45-day ceasefire in the Iran war, a move he called a "very significant step" in the conflict.

"It's a significant proposal, it's a significant step. It's not good enough, but it's a very significant step," Trump told reporters at the White House, adding that intermediaries "are negotiating now."

Iran has rejected a proposed truce in its war with the United States and Israel, state media reported Monday, despite a stark threat by U.S. President Donald Trump to destroy its vital infrastructure.

The Israeli army confirmed Monday that it attacked a day earlier a "terrorist target" in the Northern Metn town of Ain Saadeh east of Beirut, adding that reports of civilian casualties and "all details of the incident" are being reviewed.

An Israeli strike hit Beirut's southern suburbs on Monday as Israel's army said it was targeting Hezbollah, with the raid sending a large plume of smoke billowing across the skyline.

Israeli strikes in Lebanon on Sunday killed at least 15 people, a day after Israel threatened to hit Lebanon's main border crossing with Syria, forcing it to close.

Lebanese Christians marked Easter Sunday by turning their prayers to the south, where villages remain trapped by fighting between Israel and Hezbollah.

The United Nations Interim Force in Lebanon said attacks by Israel and Hezbollah near its positions "could potentially draw return fire".

Iran's Revolutionary Guards said they are completing preparations to enforce new operating conditions in the Strait of Hormuz, which has been all but shut since the war with the United States and Israel began.

U.S.-Israeli strikes killed on Monday the intelligence chief of Iran's Revolutionary Guards, the Guards said.

Iran launched fresh attacks across the Middle East on Monday and threatened "devastating" retaliation, after U.S. President Donald Trump's expletive-laced warning that Tehran must reopen the Strait of Hormuz.