US House speaker nominee Steve Scalise. (Photo: AP)

Scalise, the No.2 House Republican, had secured his party's nomination to replace ousted Speaker Kevin McCarthy but was still short of the 217 votes needed to be elected on the House floor, as several of his fellow Republicans said they would not support him.

Republicans could afford no more than four defections as they control the House by a narrow 221-212 margin if they wanted to end the House's leaderless bout that has already lasted nine days.

Republicans had hoped to avoid a repeat of the embarrassing spectacle that occurred in January, when hardline conservatives forced McCarthy to endure 15 floor votes over four days before winning the gavel.