The National Park Service issued an apology on Twitter Saturday after it retweeted messages comparing the crowd sizes at Donald Trump's and Barack Obama's presidential inaugurations.

The Park Service said the agency regrets the "mistaken" retweets from the account Friday, which were side-by-side comparisons of the size of the crowd at Obama's first inauguration and the noticeably smaller crowd Friday for Trump.

After the retweets were posted Friday, National Park Service employees were ordered to stop posting to the official agency Twitter account immediately.

"The expectation," employees were told, "is that there will be absolutely no posts on Twitter."