Washington (CNN) Two leading Senate Democrats are calling on President Donald Trump to declassify the formal notification given to Congress regarding the US drone strike that killed Iranian military commander Qasem Soleimani.

It's not publicly known what exactly is in the formal notification, though such messages to Congress typically explain legal justification for military action.

"It is critical that national security matters of such import be shared with the American people in a timely manner," says the letter, authored by Senate Minority Leader Chuck Schumer and Sen. Bob Menendez, the top Democrat on the Senate Foreign Relations Committee. "An entirely classified notification is simply not appropriate in a democratic society, and there appears to be no legitimate justification for classifying this notification."

The letter comes as Trump on Sunday signaled that he wouldn't rule out releasing some of the intelligence amid lingering skepticism from lawmakers and the public about whether the strike was justified.

"We may discuss that," he said when questioned aboard Air Force One.

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