WASHINGTON (Reuters) - Donald Trump's Republican presidential campaign, widely criticized for refusing to release the candidate's tax returns, released 10 years of returns on Friday for vice presidential nominee Mike Pence.

The Trump campaign also repeated a pledge that Trump would release his own returns once the government completes an audit.

Pence's returns for 2006 to 2015 showed the Indiana governor and former U.S. congressman paid an effective tax rate that ranged from 10 percent to 16.5 percent.

"These returns are being released with the full support of Mr. Trump who plans to release his tax returns upon completion of a routine audit," the campaign said.

Disclosure of tax returns is a standard procedure for all modern presidential candidates. Trump's critics, including the campaign of Democratic presidential nominee Hillary Clinton, have suggested he may be hiding something.

Some have speculated that Trump may pay little or no tax or that his net worth may be much less than the $10 billion he has claimed.

Pence and his wife, Karen, reported adjusted gross income over the 10 years ranging from about $113,000 last year to over $187,000 in 2009, while the effective state and federal tax rate ranged from a low of just over 10 percent in 2013 to a high of 16.5 percent in 2014, the figures show.

Charitable donations amounted to 10 percent of the family's take-home pay, equivalent to an average 7.2 percent of adjusted gross income, a statement released by the Trump campaign said.

Hillary Clinton released her 2015 tax returns last month. They showed she and her husband, former President Bill Clinton, had $10.75 million in income that year and paid an effective federal tax rate of 34.2 percent. Most of the income came from Bill Clinton's speaking fees and a book deal by Hillary.

Clinton's running mate, U.S. Senator Tim Kaine of Virginia, along with his wife, Anne Holton, released 10 years of tax returns at the same time in August. They paid a federal effective tax rate of 20.3 percent on income of about $313,000 in 2015.

(Reporting by Eric Walsh; Editing by David Gregorio)