Democratic U.S. Senate candidate Tim Kaine expressed little sympathy Monday for Republican opponent George Allen, who is facing accusations from an outside group that he's racist.

Workers' Voice, a super PAC backed by big labor, put out four racially charged web ads last week. One says Allen "hung a Confederate flag in his living room," while another resurrects "macaca," a derogatory term Allen when mocking a Democratic staffer who was videotaping a 2006 Allen campaign rally.

Kaine, who's facing more than $10 million in attack ads from outside Republican groups, said Monday that he has not seen the union's ads but that Allen could have avoided such attacks.

"I think the whole system we have that allows third-party ads should be changed, and I challenged George Allen in our first debate in December, 'Lets do a campaign that's just Kaine versus Allen and no super PACs, no third parties,'" Kaine said. "And he turned me down."

Kaine has not directly raised Allen's "macaca moment" himself, but he has said in debates that the 2006 exchange shows a pattern of divisive language by Allen. State Democrats sent out releases noting that Allen voted against making Martin Luther King, Jr. Day a federal holiday, the focus of another of the web ads from Workers' Voice.

Allen's campaign called the ads a low blow and pointed out that labor groups are working to get Kaine elected in Virginia, a right-to-work state. The ads also are distracting from real concerns of voters, they said.

"George Allen has apologized and forthrightly addresses these old accusations," spokeswoman Emily Davis said. "But when he is on the campaign trail he is hearing from Virginia families and small businesses concerned about skyrocketing fuel costs, burdensome regulations and increased taxes that are bringing uncertainty."