WASHINGTON (REUTERS) - The White House transmitted on Saturday (Jan 4) its formal notification to Congress of Friday's US drone strike ordered by US President Donald Trump that killed Iranian military commander Qassem Soleimani in Iraq, two senior congressional aides told Reuters.

Many congressional Democrats have criticised Mr Trump for failing to seek advance approval or notify Congress of the attack, which has caused a dramatic rise in tensions between Iran and the United States and its allies.

The notification was sent under a 1973 US law called the War Powers Act, which requires the administration to notify Congress within 48 hours of committing armed forces to military action or imminent actions.

Mr Trump's administration was expected to explain the circumstances, the authority under which the action was taken and the expected scope and duration of the military involvement.

The version submitted to Congress is classified and it is not clear if the White House will release an unclassified version, according to one of the aides, speaking on condition of anonymity.

The White House did not immediately respond to a request for comment.

House of Representatives Speaker Nancy Pelosi has said the strike was conducted without specific authorisation from Congress and "without the consultation of the Congress".

The Pentagon on Friday briefed staff members from the House Armed Service Committee and Senate Armed Service Committee on the attack on Friday and other recent developments in Iraq.

On Friday, Democratic US Senator Tim Kaine introduced a resolution to force a debate and vote in Congress to prevent further escalation of hostilities with Iran.