Madison's mayor and police chief Thursday called on Gov. Scott Walker to explain statements he made in a secretly recorded phone conversation that he "thought about" planting troublemakers among the thousands of demonstrators at the Capitol.

"Someone in his inner circle raised seriously the possibility of hiring people to come in and apparently create violence in my city," Mayor Dave Cieslewicz said. "I find it appalling, and I want to know who that was."

Walker spokesman Cullen Werwie said the governor had already answered questions about the phone call during a press conference Wednesday in which he acknowledged entertaining — but rejecting — the idea.

"People have brought up all sorts of different options," Walker said at the press conference. "As you saw if you've listened to the tape, we shot that down."

Tens of thousands of people have demonstrated at the Capitol over the past 11 days, during which Madison police made no arrests. Most of the demonstrators oppose a bill backed by Walker to limit collective bargaining rights for public employees.