(USA TODAY) -- An internal investigation at the Department of Veterans Affairs released today says tens of thousands of veterans waited far longer last year to receive mental health treatment than what the VA contends.

The inspector general's office found that claims by the VA that 95% of its patients are both evaluated for mental health problems and begin receiving therapy within a 14-day goal set by the department are false.

In fact, only about half of mental patients were evaluated within two weeks. The remainder waited an average of seven weeks, the investigation found.

On the time it takes to begin treatment, the probe corroborated findings by a USA TODAY analysis published Nov. 9 which revealed that about a third of VA patients wait longer than 14 days to start treatment.

The VA inspector general confirmed that only 64% are treated within 14 days, and the rest wait nearly six weeks on average before starting their treatment.

The VA's "mental health performance data is not accurate or reliable," the inspector general's report concluded, adding that the department "overstated its success."

"This report shows that the VA is failing many of those who have been brave enough to seek care," says Sen. Patty Murray, D-Wash., chairwoman of the Senate Veterans' Affairs Committee. "Once a veteran takes the step to reach out for help, we need to knock down every potential barrier to care."

With the suicide rate among veterans estimated by the VA at 18 per day, Murray, who called for the investigation, said timely mental health care "can quite frankly often be the difference between life and death."

The VA issued a statement conceding that the way it estimates timely care is flawed. "We generally agree that some revision of the metric is required," the statement says.

Department officials said last year they have had chronic difficulty monitoring access to mental health care, partly because of a 25-year-old computerized scheduling system slated for replacement in 2013.

The wars in Iraq and Afghanistan have partly resulted in an increase every three months of 10,000 new patients arriving at the VA suffering post-traumatic stress disorder.

The VA treats 1.3million mental health patients, including 400,000 from the two conflicts, according to the department.

Murray requested the investigation in November after a survey of VA mental health workers last year revealed concerns about delays and staff shortages.

The VA announced Thursday it would immediately begin expanding its 20,000-member mental health staff by 1,900 to reduce delays in care.

USA TODAY reported this month that the VA has been unable to fill about 20% of its existing psychiatric positions in many parts of the nation.

The inspector general's office stated that, according to interviews with VA staff, the "greatest challenge has been to hire and retain psychiatrists."

Three out of four hospital sites visited by investigators lacked psychiatrists.

Copyright 2012 USA TODAY, a division of Gannett Co. Inc.