WASHINGTON (AP) — The U.S. has bolstered defenses at a base in Jordan that was attacked by Iran-backed militants as it prepares for a wider U.S. response to the drone attack that killed three service members, a U.S. official said Friday.

Even as a larger U.S. military response seemed imminent, some Iran-backed factions pledged to continue to attack U.S. forces in the Middle East. In a statement released Friday, one of Iraq’s strongest Iran-backed militias, Harakat al-Nujaba, announced its plans to continue military operations against U.S. troops, despite other allied factions having called off their attacks in the wake of the Sunday drone strike in Jordan.

Some of the militias have been a threat to U.S. bases for years, but the groups intensified their attacks in the wake of Israel’s war with Hamas following the Oct. 7 attack on Israel. The war has led to the deaths of thousands of civilians in Gaza and spilled across four other countries now. Iran-backed militia groups throughout the region have used the conflict to justify striking Israeli or U.S. interests, including threatening civilian commercial ships and U.S. warships with drones or missiles in almost daily exchanges.

On Friday, the Israeli military said its Arrow defense system intercepted a missile that approached the country from the Red Sea, raising suspicion it was launched by Yemen’s Houthi rebels. The rebels did not immediately claim responsibility.

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A second U.S. official said the military had taken additional self-defense strikes inside Yemen Friday against Houthi military targets deemed an imminent threat. Al-Masirah, a Houthi-run satellite news channel, said that British and American forces conducted three strikes in the northern Yemeni province of Hajjah, a Houthi stronghold.

While previous U.S. responses in Iraq and Syria have been more limited, the attack on Tower 22, as the Jordan outpost is known, and the deaths of the three service members has crossed a line, the official said. In response, the U.S. is weighing a much wider response to include striking militia leaders. The U.S. options under consideration include targets in Syria, Yemen and Iraq, where the Iranian-made drone that killed the service members was fired from, the official said.

The attack on Tower 22 led to the first deaths of U.S. service members since the war between Israel and Hamas broke out. U.S. response options were being weighed as President Joe Biden, Defense Secretary Lloyd Austin and Chairman of the Joint Chiefs Gen. CQ Brown traveled to Dover Air Force Base in Delaware to be with the families of those fallen soldiers as they are honored at a transfer ceremony.

The U.S. has blamed the Jordan attack on the Islamic Resistance in Iraq, a coalition of Iranian-backed militias. In the days since the attack, the U.S. has bolstered the defenses around Tower 22, which houses about 350 U.S. troops and sits near the demilitarized zone on the border between Jordan and Syria. The Iraqi border is only 6 miles (10 kilometers) away.

On Thursday Defense Secretary Austin indicated that the U.S. response against the militias would widen.

“At this point, it’s time to take away even more capability than we’ve taken in the past,” Austin said in his first press conference since he was hospitalized on Jan. 1 due to complications from prostate cancer treatment.

Austin said that Iran has had a hand in the attacks by supplying and training the militias. The U.S. has tried to communicate through backchannels to Iran over the last few months to get them to rein in the militant groups, another U.S. official said.

The officials spoke on the condition of anonymity to discuss details that have not been acknowledged publicly.

The U.S. has also tried more limited military responses in a series of strikes against weapons storage sites and training areas. So far, the U.S. response has not deterred the groups, which have attacked U.S. facilities at least 166 times since October.

At least one group, Kataib Hezbollah, another powerful Iranian-backed Iraqi militia, which has been watched closely by U.S. officials, said Tuesday it would “suspend military and security operations against the occupying forces” to avoid embarrassing the Iraqi government in the wake of the Jordan attack.

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Aamer Mahdani contributed from Washington, D.C. Abdulrahman Zeyad reported from Baghdad, Jon Gambrell reported from Jerusalem and Ahmed al-Haj contributed from Yemen.