US senators on Thursday voiced outrage and demanded action over allegations that dozens of veterans died due to protracted delays at medical clinics, grilling the head of the veterans department.

Eric Shinseki, the retired general who leads the Department of Veterans Affairs (VA), faced tough questions from lawmakers at a hearing prompted by a scandal over secret waiting lists at a Phoenix hospital.

With the revelations threatening to turn into a major political headache for the White House, senators from both parties said delays for patients at veterans' hospitals have been flagged as a problem for years.

Saying she was "deeply disturbed," Senator Patty Murray said the long waiting times had "dramatically shaken many veterans' confidence in this system."

Murray said the scandal must serve as a "wake-up call" for the department.

Shinseki, who has served as the VA secretary since President Barack Obama took office in 2009, said he shared the senators' anger and was awaiting the results of an investigation by an inspector general.

"Any allegation like this . . . makes me mad as hell," Shinseki said at the start of the senate hearing. "But at the same time, it also saddens me."

The department faces charges that employees covered up long wait times at the Phoenix hospital and that the delays may have cost the lives of 40 patients.

Shinseki, a Vietnam veteran and former four-star US Army chief, promised action if the allegations are confirmed.

But a number of Republican lawmakers and some veterans' groups have called for his resignation.

Even some of Obama's fellow Democrats expressed exasperation that the secretary has not been able to turn around the department's poor track record.

Addressing Shinseki directly, Murray, a Democrat from Washington state, said: "We have come to the point where we need more than good intentions. . .what we need right now is decisive action."

Reports of neglect of veterans represented potential political dynamite for Obama, who appointed one of his senior aides, Rob Nabors, to conduct an administration review.

"While we get to the bottom of what happened in Phoenix, it's clear the VA needs to do more to ensure quality care for our veterans," Obama said in announcing the appointment.

Asked Thursday if Obama shared Shinseki's anger over the allegations, White House spokesman Jay Carney said: "He certainly is concerned and angry about the allegations we've seen."

If the charges are true, "that would be outrageous," he said.

At the hearing, Senator John McCain, a decorated Vietnam veteran, said the whole episode was a disgrace.

"We should all be ashamed," said McCain, who represents Arizona, the state where the scandal took place.

The Republican lawmaker described hosting a town hall meeting in Phoenix where families of four veterans who died recently recounted horror stories as they tried and failed to secure medical treatment for their relatives.

"With tears in their eyes, they described how their loved one suffered because they were not provided the care they needed and deserved," he said.

"They recalled countless unanswered phone calls and ignored messages, endless wait times, mountains of bureaucratic red tape, while their loved one suffered debilitating and ultimately fatal conditions."