U.S. Senate candidate Vernon Jones has accused his Democratic opponent of failing to vote for Barack Obama in the February primary.

Jones, the CEO of DeKalb County, raised the issue again Wednesday — he fired the first shot Monday — and Jim Martin skirted the subject when asked about it directly at a midday news conference.

"That is the one thing that is kind of private," Martin said at his news conference, called to announce two Fulton County officials were backing his candidacy. "A lot of things are private. It is public that I made a contribution to John Edwards."

Jones immediately focused on Martin's comments and called a 4 p.m. news conference to address the subject.

"Jim Martin did not want Senator Obama to be president and voted against him in the 2008 presidential primary," Jones said in a telephone interview before his news conference.

The two men are locked in a runoff to determine which Democrat will face Republican incumbent U.S. Sen. Saxby Chambliss and Libertarian Allen Buckley in November. The runoff is Aug. 5.

Jones' latest salvo follows Martin's repeated debate attacks, in which he has pointed out that Jones voted twice for President Bush. Jones has confirmed those ballots and said he voted for the Republican president because Bush's Democratic opponents wrote off the South.

Jones has tried to cast himself as a "conservative Democrat" in his campaign to become the state's first black U.S. senator and has dubbed Martin as "too liberal for Georgia."

Staff writer Jeremy Redmon contributed to this article.