WASHINGTON, Sept. 16 (UPI) -- A tight U.S. presidential election race is prompting special interest groups to roll out a wave of political attack ads targeting the nominees, analysts say.

Both Republican nominee Sen. John McCain of Arizona and Democratic counterpart Sen. Barack Obama of Illinois had initially discouraged such groups from launching negative ads, but with polls showing them virtually deadlocked heading into the campaign's final weeks, all bets are off, The New York Times reported Tuesday.

"I think in the next two weeks you are going to see a lot more of these coming out of the woodwork," Evan Tracey of the Campaign Media Analysis Group, told the newspaper. "They want to get messages out there that are the most disruptive politically and the closer you are to Election Day the more disruptive you are by definition."

The progressive advocacy group MoveOn announced it would launch ads tying McCain to lobbyists, while the Service Employees International Union has begun an ad campaign criticizing McCain's economic record, the Times said.

Meanwhile, the Minutemen, a group calling for stricter border security, says it is running mailers against Obama while anti-abortion rights group BornAliveTruth.org says it will run anti-Obama in New Mexico and Ohio.

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