(CNN) -- A Pennsylvania woman told police she was attacked at an ATM in Pittsburgh by a robber who became angry when he saw a John McCain bumper sticker on her car, a spokeswoman for the Pittsburgh Police Department said Thursday.

Police cannot confirm whether a man attacked this woman because she had a McCain sticker on her car.

Public Information Officer Diane Richard said police cannot substantiate her story, however, and the investigation is ongoing.

Richard said the 20-year-old told investigators a man approached her Wednesday night at an ATM in the city's East End, put a blade to her neck and demanded money.

She said she gave him $60 and stepped away from him, Richard said.

But the woman said the man "became very angry" when he noticed her car had a bumper sticker supporting the GOP presidential nominee, according to Richard. The woman said he punched her in the back of the head, knocked her to the ground and "continued to punch and kick her while threatening her," the spokeswoman said.

Before he left, the woman said, he carved the letter "B" into her face with a knife, according to Richard. There was no indication what the "B" indicated.

The alleged assailant fled on foot, Richard said.

"We, the police, cannot substantiate this yet," she said. "This is what she told police."

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The woman, who is not from Pittsburgh, refused medical attention, Richard said, although she told the investigating officer she would see a doctor Thursday. There was no update on her condition, she said.

Richard said the woman described her alleged attacker as a dark-skinned African-American, 6 feet 4 inches tall with a medium build and short dark hair, wearing dark clothing and shiny shoes.

McCain spokeswoman Jill Hazelbaker told CNN that McCain and running mate Sarah Palin "spoke to the victim and her family after learning about the incident earlier this afternoon."

Hazelbaker said the campaign would not offer more detail out of respect for the woman's privacy.

The campaign of Democratic presidential candidate Sen. Barack Obama responded to the report with a statement saying, "Our thoughts and prayers are with the young woman for her to make a speedy recovery, and we hope that the person who perpetrated this crime is swiftly apprehended and brought to justice."

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