The US has conducted major airstrikes on 85 targets in Iraq and Syria against Iranian Revolutionary Guards and affiliated militia groups in retaliation for a drone strike on an American base in Jordan last Sunday that killed three of its service members.

President Joe Biden and other top US leaders had been warning for days that America would strike back at the militias, and they made it clear it wouldn't be just one hit but a “tiered response” over time.

Biden said the US military response “will continue at times and places of our choosing.” “The United States does not seek conflict in the Middle East or anywhere else in the world. But let all those who might seek to do us harm know this: If you harm an American, we will respond,” Biden said in a statement after the US started carrying out such strikes on Friday. Biden said this past Sunday that three American soldiers were killed in Jordan by a drone launched by militant groups backed by Iran’s Islamic Revolutionary Guards Corps (IRGC).

Three US soldiers were killed and more than 40 personnel injured in a drone attack at a US base in Jordan called Tower 22.

Earlier in the day, Biden attended the dignified return of these brave Americans at Dover Airforce Base. He also spoke with each of their families.

“This afternoon, at my direction, US military forces struck targets at facilities in Iraq and Syria that the IRGC and affiliated militia use to attack US forces. Our response began today. It will continue at times and places of our choosing,” Biden said.

According to US Central Command, at 4:00 pm EST (2.30 am IST) its forces conducted airstrikes in Iraq and Syria against IRGC Quds Force and affiliated militia groups.

US military forces struck more than 85 targets, with numerous aircraft including long-range bombers flown from the United States. The airstrikes employed more than 125 precision munitions.

The facilities that were struck included command and control operations centres, intelligence centres, rockets, and missiles, unmanned aerial vehicle storages, and logistics and munition supply chain facilities of militia groups and their IRGC sponsors who facilitated attacks against US and Coalition forces, the CENTCOM said.

Defence Secretary Lloyd Austin said these strikes were at seven facilities that IRGC and affiliated militias use to attack US forces.

“This is the start of our response. The President has directed additional actions to hold the IRGC and affiliated militias accountable for their attacks on US and Coalition Forces,” he said.

“These will unfold at times and places of our choosing. We do not seek conflict in the Middle East or anywhere else, but the President and I will not tolerate attacks on American forces. We will take all necessary actions to defend the United States, our forces, and our interests,” Austin said.

The strikes on Friday were markedly more significant than previous attacks on Iranian-backed militias over the last several weeks, which have primarily focused on weapons storage or training facilities.

But the administration is threading a needle – they want to deter and stop further attacks but avoid a full-scale conflict with Iran breaking out in a region already roiled by the continuing Israel-Hamas war in Gaza, CNN said.

“We believe that the strikes were successful,” National Security Council spokesman John Kirby said.

Kirby said the US does not know now how many militants were killed or wounded. He added that US military planes were now out of harm’s way. Lt. Gen. Douglas Sims, the director of the Joint Chiefs of Staff, said Friday that the locations of the strikes were chosen “with an idea that there would likely be casualties” among the IRGC and militia personnel who use them.

B-1 bombers – long-range heavy bombers that can deploy precision and non-precision weapons –were used in the operations, a defence official told CNN. Sims said Friday that the bombers flew in a “single non-stop flight” from the US, “all of that enhanced by our Transportation Command and our ability to gas and go along the way.” Sims also said that the timing of the strikes was designed around good weather, in “an interest of ensuring that we’re hitting all the right targets.” The US strikes hit facilities used by Iranian-linked al Hashd al Shabi or Popular Mobilization Units (PMU) in the Iraqi city of Al-Qaim, located in the western part of Anbar province along the Iraq-Syria border, on Saturday morning local time, according to Iraqi security officials and the mayor of Al-Qaim.

In a statement, Yahya Rasool, a spokesperson for Iraq’s Armed Forces, decried the strikes as a “violation of Iraqi sovereignty.” “The city of Al-Qaim and the Iraqi border areas are being subjected to airstrikes by US aircraft, at a time when Iraq is striving hard to ensure the stability of the region,” Rasool said.

Iran-backed militants have targeted US military facilities in Iraq and Syria over 160 times since October, and several Republican lawmakers had called for the US to hit inside Iran directly to send a clear message.

But administration officials have been clear that any response would be proportionate so as to not further escalate things in the region.

“We don’t seek a war with Iran. We’re not looking for a wider conflict in the Middle East,” Kirby told CNN on Monday.

On Wednesday the White House said it believes an umbrella group of militants called Islamic Resistance in Iraq was behind the drone attack in Jordan.

“We believe that the attack in Jordan was planned, resourced and facilitated by an umbrella group called the Islamic Resistance in Iraq, which contains multiple groups including Kata’ib Hezbollah,” Kirby said.

He stopped short of assigning exact blame on Kataib Hezbollah, the most powerful Iran-backed militia in Iraq, saying it was not the only group responsible for previous attacks on US bases.