U.S. consumer credit shot up in June by $15.53 billion, according to a Federal Reserve report on Friday that showed consumers were willing to keep borrowing robustly in a tight job market.

June's consumer credit surge was triple the $5.08 billion increase posted in May and eclipsed forecasts by Wall Street economists for a $5-billion rise.

It was the biggest one-month gain in consumer credit in nearly four years, since a $17.29 billion jump in August 2007.

The Fed report sheds no light on whether consumers used credit out of need to pay bills or because they were motivated by optimism to spend more.

But other indicators, including government monthly retail sales data, suggested that consumers were wary about spending in June, so the big rise in consumer credit was a surprise.

Revolving credit, which mostly measures credit-card use, climbed $5.21 billion in June after a $3.32 billion gain in May. That was the biggest increase in revolving credit since March 2008.

A category called non-revolving credit, which includes such items as student loans and car loans, ballooned by $10.32 billion after a $1.76-billion rise in May.

(Reporting by Glenn Somerville, editing by Neil Stempleman)