President Biden told congressional leadership in a letter Saturday that this week’s airstrike against facilities in Syria linked to Iranian-backed militia groups was consistent with the U.S. right to self-defense.

Why it matters: Some Democrats, including Sens. Tim Kaine (D-Va.) and Chris Murphy (D-Conn.) and Rep. Ro Khanna (D-Calif.), have criticized the Biden administration for the strike and demanded a briefing.

• “Offensive military action without congressional approval is not constitutional absent extraordinary circumstances,” Kaine said Friday.
• A National Security Council spokesperson has said the Pentagon pre-notified Congress and that the administration is continuing to brief the Hill at the member and staff level.

What he’s saying: “Those non-state militia groups were involved in recent attacks against United States and Coalition personnel in Iraq,” Biden wrote in Saturday’s letter to House Speaker Nancy Pelosi and President pro tempore of the Senate Patrick Leahy.

• Biden said those attacks included the Feb. 15 “attack in Erbil, Iraq, which wounded one United States service member, wounded four United States contractors, including one critically, and killed one Filipino contractor. “
• “These groups are also engaged in ongoing planning for future such attacks,” the president added.
• “In response, I directed this military action to protect and defend our personnel and our partners against these attacks and future such attacks.”
• “The United States always stands ready to take necessary and proportionate action in self-defense, including when, as is the case here, the government of the state where the threat is located is unwilling or unable to prevent the use of its territory by non-state militia groups responsible for such attacks.”
• “I directed this military action consistent with my responsibility to protect United States citizens both at home and abroad and in furtherance of United States national security and foreign policy interests, pursuant to my constitutional authority to conduct United States foreign relations and as Commander in Chief and Chief Executive. “
• “The United States took this action pursuant to the United States’ inherent right of self-defense as reflected in Article 51 of the United Nations Charter. “
• Biden concluded by saying he was “providing this report as part of my efforts to keep the Congress fully informed, consistent with the War Powers Resolution.”

The big picture: Iran on Saturday condemned the U.S. strike in Syria, and denied responsibility for the attacks on U.S. targets in Iraq, per Reuters.

• Iranian Foreign Minister Mohammad Javad Zarif called the strike “illegal and a violation of Syria’s sovereignty,” state media reported.
• An Iraqi militia official on Friday said the strike killed at least one fighter and wounded several others, AP reports.

Go deeper: Biden says U.S. airstrike in Syria sent warning to Iran to “be careful”