The Pentagon is halting efforts to claw back recruitment bonuses paid out a decade ago to enlist troops to fight in Iraq and Afghanistan, US Defense Secretary Ashton Carter announced Wednesday, responding to public outrage.

Around 13,000 California National Guard members were involved in a probe over bonuses used as inducements during recruitment drives to overcome a shortage of troops to send to the two conflict zones, a defense official told AFP.

Of those, some 2,000 were being ordered to pay back at least $15,000 each. Around $20 million had been repaid by the time Carter made his announcement, according to the defense official. The national guard members would have faced interest charges, wage garnishments and tax liens if they refused to comply.

The Pentagon sought repayments after audits found the California National Guard had overpaid troops in an effort to meet enlistment targets.

The plight of the guard members, revealed over the weekend by the Los Angeles Times, ignited a firestorm of criticism by members of Congress and others.

"I have ordered the Defense Finance and Accounting Service to suspend all efforts to collect reimbursement from affected California National Guard members, effective as soon as is practical," Carter said in a statement.

"This suspension will continue until I am satisfied that our process is working effectively."

He noted that "many" soldiers did not know they were ineligible for the benefits they were claiming "as a result of errors and in some cases criminal behavior by members of the California National Guard."

"I want to be clear: this process has dragged on too long," Carter said in a statement.

"That's unfair to service members and to taxpayers."

It was unclear whether any of the 53 other National Guard organizations -- present in the other 49 US states plus the District of Columbia, Guam, Puerto Rico and the Virgin Islands -- also overpaid troops.

"The National Guard is looking at whether or not these kinds of issues exist elsewhere and, if so, to what extent," spokesman Jack Harrison of the National Guard Bureau told AFP.

- 'Appalled' -

Carter said he has ordered a team led by the Pentagon's personnel chief Peter Levine to come up with a process to resolve the cases by January 1, setting a July 1 deadline for making actual decisions on all cases.

The Pentagon's plans to seek reimbursement had drawn swift condemnation. The defense official acknowledged it was challenging to demand repayment from people viewed as heroes in the eyes of the public.

On Tuesday, the House Oversight Committee launched a probe, demanding the National Guard provide audits of overpayments and related documentation by November 7.

An "appalled" Democratic presidential nominee Hillary Clinton on Monday urged Congress to pass legislation to "right this wrong."

"These troops deserve our support and our deepest gratitude; they served admirably and upheld their part of the bargain," she said.

"It is unacceptable to now subject them and their families to undue financial burdens thanks to mismanagement from the California National Guard and rigid bureaucracy on the part of the Pentagon."