The United States and Britain have struck Iran-backed armed groups in Syria, Iraq and Yemen, while Israel presses ahead with its offensive against Hamas in Gaza. Here is what to know about what is happening in the region now, and why:

US ATTACKS ON GROUPS BACKED BY IRAN

Yemen's Houthis said Sunday U.S. and British air strikes "will not deter us" and vowed a response after dozens of targets were hit in retaliation for the Iran-backed rebels' repeated Red Sea attacks.

Israeli strikes across Gaza killed scores overnight as battles raged Sunday in the besieged territory's south and Hamas was reviewing a proposal for a halt in the nearly four-month-long war.

The head of Iraq's pro-Iran Hashed al-Shaabi alliance on Sunday demanded the withdrawal of U.S.-led coalition forces from the country following deadly strikes.

The U.S. military overnight launched an air assault on dozens of sites in Iraq and Syria used by Iranian-backed militias and the Iranian Revolutionary Guard, in the opening salvo of retaliation for the drone strike that killed three U.S. troops in Jordan last weekend.

The massive barrage of strikes hit more than 85 targets at seven locations, including command and control headquarters, intelligence centers, rockets and missiles, drone and ammunition storage sites and other facilities that were connected to the militias or the IRGC's Quds Force, the Guard's expeditionary unit that handles Tehran's relationship with and arming of regional militias. And President Joe Biden made it clear in a statement that there will be more to come.

Hamas officials said that the group is studying a proposed cease-fire deal that would include prolonged pauses in fighting in Gaza and swaps of Israeli hostages for Palestinian prisoners, but the militants appeared to rule out some key components.

Hamas remains committed to its initial demands for a permanent cease-fire, the group's top political leader Ismail Haniyeh and a senior Beirut-based official, Osama Hamdan, said. Hamdan also said the group seeks the release of thousands of Palestinian prisoners being held for acts related to the conflict with Israel, including those serving life sentences.

The U.S. military launched an air assault on dozens of sites in Iraq and Syria used by Iranian-backed militias Friday, in the opening salvo of retaliation for the drone strike that killed three U.S. troops in Jordan last weekend, officials told The Associated Press.

President Joe Biden and other top U.S. leaders have been warning for days that the U.S. would strike back at the militias, and they made it clear that it wouldn't be just one hit, but would be a "tiered response" over time. The officials spoke on condition of anonymity to discuss military operations not yet made public.

Three pro-Iran fighters were killed in Israeli strikes south of Damascus Friday, a war monitor said, with Iranian media reporting an adviser from the Revolutionary Guards was among the dead.

The Syrian Observatory for Human Rights said "three members of pro-Iran groups, including an Iranian and an Iraqi" were killed in "Israeli air strikes".

Iraq's pro-Iran Al-Nujaba movement said Friday it intends to press on with attacks on U.S. troops in the Middle East, despite Washington's threat to hit back after three of its soldiers were killed in Jordan.

"Any (U.S.) strike will result in an appropriate response," Al-Nujaba leader Akram al-Kaabi said in a statement, adding the group would continue its actions until its demands are met for U.S. troops to leave Iraq and an end to Israel's war on Hamas in Gaza.

Defense Secretary Lloyd Austin has said it's time to further disable Iran-backed militias that have struck at U.S. forces and ships in the Middle East and the U.S. is preparing to take significant action in response to the deaths of three U.S. service members in Jordan.

For days the U.S. has hinted strikes are imminent. While the threat of retaliation for Sunday's deaths has driven some militant groups to say they were stopping hostilities, as late as Thursday Yemen's Houthi rebels were still attacking vessels and fired a ballistic missile at a Liberian-flagged container ship in the Red Sea.