(CNN) The Trump administration sent Congress a formal notification Saturday regarding the drone strike ordered by President Donald Trump this week that killed Iranian military commander Qasem Soleimani, according to a top Democratic aide and a senior White House official.

White House officials told lawmakers on Friday the notification would be sent in accordance with the law. The notice must be sent within 48 hours of US forces entering into hostilities in accordance with the War Powers Act -- a series of procedural requirements to ensure that presidents keep Congress apprised of military decisions.

The notification sent to Congress is classified, according to the Democratic aide. In the past there have also been declassified versions sent in tandem, but it's unclear if the White House plans to also do that, the Democratic aide said.

House Speaker Nancy Pelosi said in a statement Saturday that the White House's notification "raises more questions than it answers," pointing to the decision to classify it as a "highly unusual" move that "compounds our many concerns, and suggests that the Congress and the American people are being left in the dark about our national security."

"The Trump Administration's provocative, escalatory and disproportionate military engagement continues to put servicemembers, diplomats and citizens of America and our allies in danger.," Pelosi said in the statement. "This initiation of hostilities was taken without an Authorization for Use of Military Force (AUMF) against Iran, without the consultation of the Congress and without the articulation of a clear and legitimate strategy to either the Congress or the public."

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