The US budget deficit grew to $666 billion in fiscal year 2017, up 13.6 percent from the year before, according to official data released Friday.

The deficit now accounts for 3.5 percent of gross domestic product, up from 3.2 percent in 2016. 

"Growth in spending outpaced growth in tax receipts for the second year in a row as a result of historically subpar economic growth," a Treasury Department statement said.