WASHINGTON —  Just kidding.

John Kerry (search) told a Detroit radio station on Friday he'd name his running mate "in a matter of days," throwing the Washington rumor mill into high gear. Later in the day, he grinned when told that his interview was taken seriously.

"All you have you do is listen to it," Kerry said aboard his campaign plane. "It was plain (that it was a joke). Don't ever write about me being dour and sober and somber."

"There is no announcement imminent," Kerry spokeswoman Stephanie Cutter said. "And we won't have more to say on the subject until Senator Kerry makes a decision on who is the best possible running mate."

Democrats say they've been told by the campaign not to expect Kerry's choice until next month.

In an interview with WJR in Detroit, Kerry was asked who he was considering for vice president (search).

"Yeah, we'll have that done very, very shortly. We've really got most of them in place and we're on the short list and we'll have it done in a matter of days," Kerry replied.

Asked if he would announce the choice on he show, the senator said sarcastically: "Yeah, absolutely. That was my plan, and let me see now, I'll run through the list."

"Senator Kerry was just making a joke after the radio host asked if he'd make his announcement on the radio show," Cutter said.