U.S. President Joe Biden looked to send a message to Iran by authorizing air strikes in Syria on Thursday, February 25: "You can't act with impunity, be careful."

His comments to reporters on Friday came a day after the U.S. military struck a site in Syria used by two Iranian-backed militia groups in response to rocket attacks on American forces in the region in the past two weeks, generating concern among lawmakers who said Biden had not asked for the necessary congressional authorization, CNN says.

"Up to a handful" of militants were killed in the strikes, a U.S. official said. The site was not specifically tied to the rocket attacks, but Secretary of Defense Lloyd Austin said he was "confident" it was used by the same Iranian-backed Shia militias targeting US and coalition forces in Iraq with rocket attacks.

The site is believed to be used as part of a weapons smuggling operation by the Iranian-backed militias, according to a U.S. official. The site was used by Iraqi Hezbollah militias near al-Hurri village right on the Syrian-Iraqi borders inside Syria, a resident in Albu Kamal city said under the condition of anonymity for security reasons.

The administration has asserted that the strike was backed by Article II of the Constitution, as well as the Charter of the United Nations. Pentagon spokesman John Kirby said the strikes took place "at President Biden's direction" and were authorized not just to respond to the recent attacks against American and coalition forces but also to deal with "ongoing threats to those personnel."