US launched air strikes in retaliation for injured soldiers in Iraq, and Iran vowed "revenge" for its top man in Syria killed allegedly by Israel, escalating Mideast tensions.

Monday began with the news of multiple attacks on US forces in Iraq by Iran-backed groups. Then Israelis killed a top IRGC commander in Syria, drawing a harsh response from Iran that Israel “will pay” for it. Then the Pentagon announced airstrikes on Iran-backed forces in Iraq, confirming that an American serviceman had been critically injured in the earlier attacks.

Belligerent statements came aplenty.

“These strikes are intended to… degrade their ability to continue attacks,” said US CENTCOM commander General Michael Erik Kurilla. "These strikes are intended to hold accountable those elements directly responsible for attacks on coalition forces in Iraq and Syria and degrade their ability to continue attacks. We will always protect our forces," he emphasized in a statement.

“The usurper and savage Zionist regime will pay for this crime,” read the IRGC statement on the killing of Razi Mousavi, its top military and intelligence man in Syria. “A line has been crossed,” announced Hezbollah in a typically vague, non-committal response.

Late Monday evening, as the US forces were hitting Iran-affiliated targets in Iraq, dozens of Basiji ‘ultras’ gathered in front of Iran’s National Security Council in Tehran to demand a swift and hard response to the Israeli killing of the IRGC’s commander in Syria.

Razi Mousavi (aka Seyyed Razi) headed IRGC’s ‘logistics’ and military coordination in Syria, which may be better understood as being in charge of getting weapons or money for Iran-backed forces in Syria and Lebanon.

The Iranian state TV interrupted its programs to announce his death, a rare event in cases of other casualties in Syria.

IDF spokesperson Rear Admiral Daniel Hagari said, "I won't comment on foreign reports, these or others in the Middle East," in response to a reporter's question at a nightly press conference. "The Israeli military obviously has a job to protect the security interests of Israel."

Images emerged of him alongside Qasem Soleimani, the former head of the IRGC Quds Force who was killed by a US drone attack in January 2020. The images were there as evidence of Mousavi’s stature and the significance of his loss.

“[Mousavi] was one of the best of brothers who worked to support the Islamic resistance in Lebanon for decades of his honorable life,” said Hezbollah in a statement. “We consider this assassination a blatant and shameless attack. And exceeding the limits.”

Razi Mousavi had been active in Syria for more than 25 years, and had escaped multiple Israeli attempts on his life, according to reports in IRGC-affiliated media.

His death is a clear blow to the IRGC’s operations in Syria and beyond. What is not clear is how the Iranian regime will respond beyond issuing threatening statements.

It may pressure its allied groups (in Yemen, Iraq, and Lebanon) to increase aggression against Israel and the US interests. Or it might strike directly, which would take the current conflict, that began with Hamas rampage of Israel and Israel’s onslaught on Gaza, to a whole new level.

So far, only Yemen's Houthis have officially entered the war in support of Hamas. Hezbollah, by far the strongest non-state actor in the region, has had no more than limited exchanges of fire with Israeli forces across the border. Perhaps most crucially, the Biden administration has tried hard to prevent a full-blown war that would drag its forces into a costly war during an election year.

All that could change if the regime in Iran follows on its words with action.

It did just that when Soleimani was killed. But the Hard Revenge promised to the hardline supporters of Supreme Leader Ali Khamenei, turned out to be a ‘token’ attack on a US base in Iraq, allegedly, after notifying the Americans.

That was a New Year's victory for Trump on January 3 2020. This could be a Christmas headache for Biden.