The share of Americans behind on their student loan payments jumped over the past year despite the improving economy, new data released Thursday show.

About 11.5 percent of outstanding student debt was at least 90 days late or in default as of June 30, up from around 10.9 percent at the same time last year, according to the Federal Reserve Bank of New York. The New York Fed estimates that nearly one in four borrowers whose loans have come due are severely delinquent, or double the published rate, because nearly half of student debt doesn't presently require a monthly payment.

By contrast, the share of total household debt in distress fell to 3.98 percent, New York Fed data show. The figure hasn't been below 4 percent since 2007.

At roughly $136 billion, the total amount of student debt that's severely delinquent or in default is more than all other distressed non-mortgage debt combined, a reversal from last year, New York Fed data show. Non-mortgage debt carried by households includes auto loans, credit cards, home equity lines of credit and other personal loans.

The increase in student debt woe comes despite a growing U.S. economy that's adding jobs and raising workers' wages. Student debt pain also is spreading despite a significant jump in the number of borrowers enrolled in generous government programs that allow them to make payments on their federal student loans based on their earnings, and high-level attention from the White House to fix what President Barack Obama described in 2013 as a "crisis in terms of college affordability and student debt."

The new data is fueling concerns among those outside the student loan industry that student debt will crimp economic growth for years to come as households cut back on spending and investments to service their growing pile of college debt. The New York Fed estimates there's roughly $1.2 trillion in outstanding student debt spread across more than 43 million borrowers. Average debt burdens have nearly doubled over the past decade.

"Some in the student loan industry still believe that things are just fine and dandy. But the reality is that millions of borrowers are needlessly in distress," said Rohit Chopra, formerly the top student loan official at the federal Consumer Financial Protection Bureau.

About 90 percent of outstanding student debt is either owned or insured by the federal government. Virtually all borrowers with federal student loans are eligible for repayment plans that enable them to make payments based on their monthly take-home pay.

The increase in distress despite the availability of income-linked repayment plans for roughly 90 percent of the market signals that perhaps poor loan servicing is to blame. Loan servicers collect borrowers' monthly payments and counsel them on their repayment options.

"When borrowers reach out for help, student loan servicers need to own up to borrowers and tell them the truth about their options, rather than steering them into a plan that gets them off the phone quickly," Chopra said.

He added that of the more than 8 million Americans in default on a student loans, "most of these defaults could have been avoided if servicers enrolled borrowers in affordable repayment plans."

Servicers have previously argued that when they get in touch with borrowers, they usually help them avoid default.

More than 7 million of those defaults are on loans owned or guaranteed by the Education Department. The department, led by Secretary Arne Duncan, has been pushing its loan servicers to improve their treatment of borrowers. Obama ordered Duncan and other high-ranking officials earlier this year to explore new ways to stem what New York Fed data suggest is a rising tide of defaults.

This year, and in each of the preceding three years, about $28 billion of previously current student debt fell into delinquency every quarter, New York Fed data show. The annual average has barely budged since the start of 2012, despite the improved economy and healthier household finances.

The New York Fed's figures are among the most comprehensive data sets available on student loans, but the information isn't perfect. The Huffington Post in March detailed the data's shortcomings. And earlier this month, in an acknowledgement that the federal government is still trying to figure out student debt and the possible problems it poses, the Federal Reserve in Washington revised down its estimate of total student debt by about 7 percent.