(CNN) -- The founder and former CEO of Black Entertainment Television apologized Thursday to Sen. Barack Obama for what appeared to be veiled comments this week regarding the Democratic presidential hopeful's acknowledged drug use as a teenager.
Bob Johnson, a high-profile supporter of Sen. Hillary Clinton, said he sent Obama a letter and also was reaching out by phone.
Obama spokesman Bill Burton responded Thursday afternoon, saying, "Obama accepts the apology. We're going to leave it at that."
Johnson drew criticism following remarks he made Sunday at a Clinton campaign stop in Columbia, South Carolina.
In defending the civil rights record of the former first lady and President Clinton, Johnson said, "As an African-American, I'm frankly insulted that the Obama campaign would imply that we are so stupid that we would think Bill and Hillary Clinton, who have been deeply and emotionally involved in black issues when Barack Obama was doing something in the neighborhood that -- and I won't say what he was doing, but he said it in his book -- when they have been involved." Watch what Johnson said about Obama »
Many political observers said they thought Johnson was referring to Obama's drug use, which the senator wrote about in his 1995 memoirs, "Dreams From My Father."
Shortly after Johnson's remarks, the Clinton campaign released a statement from him saying he had been "referring to Barack Obama's time spent as a community organizer and nothing else. Any other suggestion is simply irresponsible and incorrect."
The Obama campaign did not accept his explanation.
"His tortured explanation doesn't hold up against his original statement. And it's troubling that neither the campaign nor Sen. Clinton -- who was there as the remark was made -- is willing to condemn it as they did when another prominent supporter recently said a similar thing," said Burton, the Obama spokesman.
In December, Bill Shaheen resigned as the co-chairman of Clinton's state campaign in New Hampshire after telling The Washington Post that Republicans probably would use Obama's past drug use against him if he were to become the Democratic presidential nominee.
Johnson is not a paid staffer but a high-profile volunteer and wealthy fundraiser for the senator from New York.
Asked Tuesday at a Las Vegas, Nevada, debate about Johnson's comments, Clinton distanced herself from his remarks, saying, "Well, Bob has put out a statement saying what he was trying to say and what he thought he had said. And we accept him on his word on that."
But when asked whether Johnson's comments were out of bounds, Clinton said, "Yes, they were. And he has said that."
Johnson said Clinton did not ask him to apologize or leave the campaign. Johnson said he quickly realized his comments were a mistake "made in haste in an attempt to be funny."
Earlier this week, Clinton and Obama both called for an end to the bitter, racially charged exchanges that have taken place between their campaigns in recent days. Watch Obama, Clinton call for a truce »
Sunday's flare-up capped days of sparring that began with Clinton's comments last week that while the Rev. Martin Luther King Jr. led the civil rights movement, "Dr. King's dream began to be realized when President Lyndon Johnson passed the Civil Rights Act of 1964. It took a president to get it done."
Some African-American leaders criticized the remarks as dismissive of the civil rights movement and of King, who was assassinated in 1968.
Clinton's campaign had accused the Obama camp of distorting recent remarks by her and her husband that touched off concerns among some African-American voters.
Obama has described Hillary Clinton's comments about King as "ill-advised" but rejected any suggestion his campaign was behind the complaints.
But Monday night, hours after both sides tried to lower the rhetoric, U.S. Rep. Charlie Rangel, D-New York, called Obama "absolutely stupid" for attacking Clinton for her comments about Lyndon Johnson and King.
"How race got into this thing is because Obama said 'race,' " said Rangel, a Clinton supporter and one of the highest-ranking African-Americans in Congress, in a TV interview on NY1. Watch Rangel react to Obama »
Johnson's apology comes as both the Clinton and Obama campaigns step up their efforts to win South Carolina's coveted African-American vote. Nearly 50 percent of the likely Democratic voters in the state are African-American. Both campaigns are rolling out high-profile black leaders and celebrities leading up to the state's January 26 Democratic primary.
In Johnson's letter to Obama he wrote, "I'm writing to apologize to you and your family personally for the uncalled-for comments I made at a recent Clinton event. In my zeal to support Senator Clinton, I made some very inappropriate remarks for which I am truly sorry. I hope that you will accept this apology. Good luck on the campaign trail." E-mail to a friend