Republican presidential candidate Mitt Romney paid a lower federal tax rate than his running mate, Rep. Paul Ryan, the last two years.

Ryan paid an effective federal tax rate of 15.9 percent in 2010 and 20 percent in 2011, according to tax returns released by the Romney campaign Friday evening.

In 2010, Ryan and his wife reported an adjusted gross income of a little more than $215,000. Most of that came from Ryan's congressional salary. They paid more than $34,000 in federal taxes on that income. They also paid $3,168 in employment taxes for a household worker.

Romney's tax returns have become a distraction for his campaign, with Democrats and even some fellow Republicans urging Romney to release more than two years of his returns.

Romney said Thursday he has paid at least 13 percent of his income in federal taxes in each of the past 10 years.