U.S. B-2 stealth bombers struck weapons-storage sites linked to Houthi rebels in Yemen, the latest effort to blunt attacks by the Iran-backed group that have disrupted commercial shipping in the Red Sea.

The strikes hit bunkers containing missiles and other munitions “used to target military and civilian vessels throughout the region,” U.S. Central Command said today. U.S. Air Force and Navy personnel took part in the operation and there’s no indication of civilian casualties, it added.

The U.S. and its allies have repeatedly struck the Houthis, who started attacking ships in the Red Sea and Gulf of Aden after Israel began its war against Hamas in Gaza just over a year ago. The group is one of a number of militant groups backed by Iran, alongside Hamas and Hezbollah in Lebanon, who are at various stages of conflict with Israel.

The Houthis, who reported no casualties, said U.S. and UK strikes hit the capital Sanaa and the Saada governorate. The group was designated a terrorist organization by the U.S. earlier this year.

The use of B-2 bombers was intended to send a message, according to Defense Secretary Lloyd Austin.

“This was a unique demonstration of the United States’ ability to target facilities that our adversaries seek to keep out of reach, no matter how deeply buried underground, hardened, or fortified,” he said.

The message may have been intended for Iran, which has moved much of its nuclear program below ground in recent years. The B-2 is the only U.S. aircraft equipped to use the Massive Ordnance Penetrator, a bomb that the airforce says is specifically designed to destroy “adversaries’ weapons of mass destruction located in well protected facilities.”

The comments came as Israel weighs a response to Tehran for the firing of 200 ballistic missiles at the country more than two weeks ago. The U.S. has been urging Prime Minister Benjamin Netanyahu’s government to avoid striking oil or nuclear targets.

Iran’s Foreign Minister, Abbas Araghchi, met Egyptian President Abdel Fattah El-Sisi in Cairo as he continued an intense round of shuttle diplomacy aimed at stopping Israel’s military operations in Gaza and Lebanon.

Araghchi has already visited Saudi Arabia, Qatar, Oman and Jordan. His stop in Cairo marks the first time an Iranian foreign minister has visited Egypt in more than a decade, underscoring the extent to which its current standoff with Israel has drawn Tehran closer to is Arab neighbors.

Despite numerous strikes on the Houthis, the allies have been unable to halt its attacks. In a June assessment, American intelligence officials said Houthi assaults on commercial vessels in the Red Sea led to a 90% decline in container shipping through the area between December and February.

Earlier: Houthi Attacks on Red Sea Disrupt Global Trade, U.S. Spies Say

Israel said it intercepted a drone that approached its territory from the Red Sea overnight.

The B-2s flew to their targets from Whiteman Air Force Base in Missouri. It marked the first time since January 2017 that the wing-shaped stealth bomber has flown a combat mission. Back then, two B-2s flew a 30-hour round-trip mission to bomb an Islamic State training camp in Libya.

Each B-2 is capable of carrying as much as 20 tons of bombs, including 80 500-pound GPS-guided munitions.