Veterans' health care is a "high risk" budget issue that threatens to cost taxpayers tens of billions of dollars unless longstanding problems are addressed, government auditors warned Wednesday.

The nonpartisan Government Accountability Office said health care costs at the Department of Veterans Affairs have nearly tripled since 2002 -- to more than $59 billion a year -- as a result of the Iraq and Afghanistan wars and the aging of Vietnam-era veterans.

Costs are likely to continue to rise as the VA responds to "serious and longstanding problems with veterans' access to care," the GAO said.

The report praised a new law overhauling the VA in the wake of a scandal over long wait times for veterans seeking care. But it said officials must ensure that veterans obtain needed care, whether from the VA or from outside providers authorized under the 2014 law.

"While timely and cost-effective access to needed health care services is essential, it also is imperative that VA ensures the quality and safety of the services it provides," the report said.

The GAO report, issued every other year, identified 32 "high risk" areas that could cause significant budget problems due to waste, fraud, mismanagement or structural flaws. The list includes Medicare and Medicaid, as well as a host of Pentagon and nuclear security programs and the national flood insurance program, among others.

In 2013, the GAO added climate change to the high-risk list.

The GAO report is the latest in a series of reports and investigations highlighting problems at the VA, which has been under intense scrutiny since a whistleblower reported last year that dozens of veterans died while awaiting treatment at the Phoenix VA hospital, and that appointment records were manipulated to hide the delays.

The scandal led to the ouster of then-VA Secretary Eric Shinseki and to a new law making it easier for veterans to get VA-paid care from local doctors, and making it easier to fire poor-performing executives.

A report by the VA's inspector general last year said workers falsified waitlists while their supervisors looked the other way or even directed it, resulting in chronic delays for veterans seeking care and bonuses for managers who appeared -- falsely -- to meet on-time goals.

The VA said in a statement Wednesday that it shares GAO's goal and is working of ensuring veterans receive high-quality health care.

"We realize we need to make significant improvements," spokesman James Hutton said, noting that VA recently began a reform effort to address many of the concerns identified by the GAO.

The restructuring, nicknamed "MyVA," is designed to provide veterans with a positive customer service experience, regardless of whether they use the department's website, call their local VA office or walk into a clinic, VA Secretary Robert McDonald said.

As the nation emerges from the longest war in its history in Afghanistan, "VA is emerging from one of the most serious crises the department has ever experienced," McDonald told Congress Wednesday. "We now have before us the greatest opportunity we've ever had to improve care for veterans ... and make the VA a model agency with respect to customer experience and stewardship of taxpayer resources."

Besides the overhaul adopted last year, Congress recently approved a bill to combat a suicide epidemic that claims the lives of an estimated 22 veterans every day. President Obama is expected to sign the measure on Thursday.