Updated April 12, 3 p.m.

Texas Railroad Commission Chairman Barry Smitherman apologized on Friday for weighing in on the gun-control developments in Washington on Thursday by retweeting an image that showed a noose beside the names of Republican U.S. senators who had voted down a filibuster.

"In my desire to identify the 16 senators who voted against the [Second Amendment]," he tweeted, "I chose the wrong message to [retweet]. A regretful mistake. I apologize."

On his website, he added a longer statement:

"Over the past several months, I have begun using Twitter as a tool to engage with a more politically active and attuned group of voters. I have enjoyed the conversation. Twitter remains a medium I am committed to. Last night, as conservatives across the nation erupted in outrage, I reacted to a capitulation by 16 Republican member of the U.S. Senate on the 2nd Amendment. Working from my iPhone, I grabbed a readily available listing of those senators, and sent it as a re-tweet. In my haste to post, I failed to carefully review the complete image. The choice of a message to re-tweet was wrong. I have pulled the material down. Even the original author of the post has withdrawn the material. The mistake was mine. I apologize."

Original story:

Texas Railroad Commission Chairman Barry Smitherman weighed in on the gun-control developments in Washington on Thursday, retweeting an image that showed a noose beside the names of Republican U.S. senators who had voted down a filibuster.

On Twitter, Smitherman re-posted an image and message from a user with the handle @PsychScriv, who had posted: “Make sure none of these people have seats in 2014.” The accompanying image showed a list of the 16 Republican senators whose vote had broken the filibuster that would have kept the gun-control bill off the U.S. Senate floor. A noose dangled beside the names, topped by a single word: “Treason.”

Smitherman added his own commentary, tweeting: "We are in trouble when these Rs side w/ Sen Reid." The list included Sen. Tom Coburn, R-Okla., and Sen. John McCain, R-Ariz., the Republican party's 2008 presidential nominee.

The liberal group Progress Texas decried Smitherman's post and called for an apology. "Barry Smitherman's reprehensible action is disturbing, disgusting and has absolutely no place in our political discourse," Matt Glazer, the group’s executive director, wrote in a statement. "To suggest that any American, let alone a U.S. senator, deserves to be hung for a democratically cast vote is absolutely unacceptable." A call to Smitherman's cellphone on Thursday night was not immediately returned. He posted several subsequent messages, including two retweets of U.S. Sen. Ted Cruz, R-Texas, on the gun issue. Smitherman, who leads the board that regulates the state's oil and gas industry, was appointed to the Railroad Commission by Gov. Rick Perry in 2011 and won election to the office last November. He has made headlines in recent months by launching a course for Railroad Commission employees with concealed handgun licenses. He also recently launched a glossy new website, barryfortexas.com.