Three overnight airstrikes on eastern Syria Saturday near a strategic border crossing with Iraq killed six Iran-backed militants, two members of Iraqi militia groups told The Associated Press.

The strikes on the border region of Boukamal came hours after an umbrella group of Iran-backed Iraqi militants — known as the Islamic Resistance — claimed an attack on a U.S. military base in the city of Irbil in northern Iraq. The group has conducted over a hundred attacks on U.S. positions in Iraq and eastern Syria since the onset of the Hamas-Israel war on October 7.

Four of the dead were from Lebanon’s powerful Hezbollah group, while the other two were Syrian, the militants said. They spoke on condition of anonymity because they were not cleared to talk to the press. Another two were injured, they said.

Meanwhile, an activist collective that covers news in the area, Deir Ezzor 24, said the airstrikes hit two militant posts and a weapons warehouse that it says was recently stocked with rocket launchers and munitions.

Elsewhere, Britain-backed opposition war monitor the Syrian Observatory for Human Rights said in addition to the weapons warehouse, the strikes targeted a militants’ convoy that had arrived from Iraq to Syria as well as a location where a militia affiliated with Iran’s paramilitary Revolutionary Guard was training.

It added that the strikes killed nine people — three Syrians and six people from other nationalities.

Washington did not immediately comment on the strike, although it has announced some were planned on Iran-backed militia positions following the surge of attacks over the past two months.

President Joe Biden last week ordered the U.S. military to carry out strikes on Iranian-backed Iraqi groups following a rocket attack that wounded three U.S. troops.

The spike in tension has put Baghdad in a delicate situation. Iraqi Prime Minister Mohammed Shia al-Sudani has tried to ease the strain between the militant groups that helped him reach power and the United States, where Iraq’s foreign reserves are housed.