Iranian-backed militants in Iraq and Syria have long battled with U.S. and coalition forces, launching sporadic attacks against bases in the region where troops are deployed to fight Islamic State group insurgents.

But since Oct. 17, as civilian deaths in Israel's war against Hamas began to skyrocket, there has been a dramatic spike in attacks by Iran's proxies, operating under the umbrella name of the Islamic Resistance in Iraq.

While most of the more than five dozen attacks have been largely ineffective, at least 60 U.S. personnel have reported minor injuries. Most often those have been traumatic brain injuries from the explosions, and all troops have returned to duty, according to the Pentagon.

In response to the attacks, the U.S. has walked a delicate line. The U.S. military has struck back just three times as the Biden administration balances efforts to deter the militants without triggering a broader Middle East conflict.

A look at the attacks and the U.S. response:

Attacks - When, Where, Why

According to the Pentagon, Iranian-backed militants have launched 61 attacks on bases and facilities housing U.S. personnel in Iraq and Syria since Oct. 17. Of those, 29 have been in Iraq and 32 in Syria.

The U.S. has about 2,000 U.S. forces in Iraq, under an agreement with the Baghdad government, and about 900 in Syria, mainly to counter IS but also using the al-Tanf garrison farther south to keep tabs on Iranian proxies moving weapons across the border.

The latest jump in attacks began 10 days after Hamas' Oct. 7 incursion into Israel, where at least 1,200 people were killed. Israel's blistering military response has killed thousands of civilians trapped in Gaza and fueled threats of retaliation by a range of Iran-backed groups, including Hezbollah in Lebanon, Yemen-based Houthis, and militants in Iraq and Syria. Those threats escalated after an Oct. 17 blast at a Gaza hospital killed hundreds of civilians. Hamas blamed Israel for the explosion, but Israel has denied it, and both Israeli and U.S. officials have blamed it on a missile misfire by Islamic Jihad.

The bulk of the attacks on bases and facilities have been with one-way suicide drones or rockets, and in most cases there were no injuries and only minor damage. A significant number of the injuries, particularly the traumatic brain injuries, were in the initial attacks between Oct. 17 and 21 at al-Asad air base in Iraq and al-Tanf. One U.S. contractor suffered a cardiac arrest and died while seeking shelter from a possible drone attack.

Who are these groups?

With a power vacuum and years of civil conflict following the 2003 U.S.-led invasion of Iraq, militias grew and multiplied in Iraq, some supported by Iran. A decade later, as the Islamic State extremist group swept across Iraq, a number of Iran-backed militias came together under the Popular Mobilization Forces umbrella group and fought IS.

The groups included the Asaib Ahl al-Haq, the Badr Brigades and Kataeb Hezbollah, or Hezbollah Brigades - a separate group from the Lebanese Hezbollah. A number of the Iraqi militias also operate in Syria, where Iran supports the government of Bashar Assad against opposition groups in the uprising-turned-civil-war that began in 2011.

After the outbreak of the Israel-Hamas war, a group of the Iran-backed factions branded itself under the new Islamic Resistance in Iraq name, and began the latest spate of attacks on bases housing U.S. forces in Iraq and Syria.

The attacks put Iraqi Prime Minister Mohammed Shia al-Sudani in a difficult position. While he came to power with the Iranian-backed groups' support, he also wants continued good relations with the U.S. and has backed the ongoing presence of American troops in his country.

U.S. Secretary of State Antony Blinken, in a meeting with al-Sudani this month, warned of consequences if Iranian-backed militias continued to attack U.S. facilities in Iraq and Syria. Al-Sudani then traveled to Tehran and met with Iran's Supreme Leader Ayatollah Ali Khamenei, a meeting U.S. officials suggested was a positive development.

An official with one of the Iranian-backed militias said al-Sudani put "great pressure" on the militias not to carry out attacks during Blinken's visit. In return, he said, al-Sudani promised to push the Americans not to retaliate aggressively against militias that have carried out the strikes. The official spoke on condition of anonymity because he was not authorized to comment publicly.

Proportional or not enough?

Since the Oct. 7 Hamas attack, the Biden administration has moved warships, fighter jets, air defense systems and more troops into the Middle East in a campaign to discourage militant groups from widening the conflict.

But the U.S. military response to the attacks on its forces has been minimal. On Oct. 27, U.S. fighter jets struck two weapons and ammunition storage sites in eastern Syria near Boukamal that were used by Iran's Islamic Revolutionary Guard Corps and Iranian-backed groups. On Nov. 8, fighter jets dropped bombs on an IRGC weapons storage facility near Maysulun in Deir el-Zour. And on Nov. 12, U.S. airstrikes targeted a training facility and a safe house in the Bulbul district of Mayadin. U.S. officials said IRGC-related personnel were there and likely struck, but provided no details.

There are concerns within the administration that more substantial retaliation could escalate the violence and trigger more deadly attacks. The Pentagon says the strikes have degraded the group's military stockpiles and made the sites unusable.

But critics argue that the U.S. response pales in comparison with the 60 attacks and American injuries, and - more importantly - has obviously failed to deter the groups.

Iraq Government Sensitivities

Though nearly half of the attacks have been on U.S. bases in Iraq, the U.S. has conducted retaliatory airstrikes only against locations in Syria.

The Pentagon defends the strike decisions by saying the U.S. is hitting Iranian Revolutionary Guard sites, which has a more direct impact on Tehran. Officials say the goal is to pressure Iran to tell the militia groups to stop the attacks. They also say the sites are chosen because they are weapons warehouses and logistical hubs used by the Iran-linked militias, and taking them out erodes the insurgents' attack capabilities.

A key reason the U.S. is concentrating on Syria, however, is that the U.S. doesn't want to risk alienating the Iraqi government by striking within its borders - potentially killing or wounding Iraqis.

In early January 2020, the U.S. launched an airstrike in Baghdad, killing Gen. Qassim Soleimani, the head of Iran's elite Quds Force, and Abu Mahdi al-Muhandis, deputy commander of Iran-backed militias in Iraq. The strike frayed relations with the Iraqi government and spawned demands for the withdrawal of all U.S. forces from the country.

The U.S. considers its presence in Iraq as critical to the fight against IS, its ability to support forces in Syria and its ongoing influence in the region. Military leaders have worked to restore good relations with Baghdad, including providing ongoing support for Iraqi forces.

From the Associated Press