The US Army could be reduced by a further 15 percent, with cuts to the numbers of full-time active soldiers as well as reserves, Defense Secretary Chuck Hagel said Wednesday.

He said a review found that priority missions could be handled with between 420,000 and 450,000 active troops -- compared to the 490,000 currently envisaged after cuts.

Presenting the results of a study to reporters at the Pentagon, Hagel said the additional cuts would help him make $150 billion in savings at a time when budgets are tight.

But he warned that even with an additional 15 percent reduction in troop numbers, the Pentagon would not be able to meet the savage spending cuts imposed on it by the so-called "sequester."

This draconian package of across the board funding reductions was a result of Congress failing to agree a budget, and has forced the Defense Department to furlough thousands of civilian workers.

"One option the review examined found that we could still execute the priority missions determined by our defense strategy while reducing army end-strength to between 420,000 and 450,000 in the active component and between 490,000 and 530,000 in the Army reserves," he said.

"Similarly, the Air Force could reduce tactical aircraft squadrons - potentially as many as five - and cut the size of the C-130 fleet with minimal risk," he said, referring to the military's workhorse transport plane.

But he said that the review had also laid out two more dramatic options for meeting the budget cuts demanded under the sequester.

The only way that this could be done, he said, would be by dramatically reducing the size of the armed forces or by halting technological modernization programs.