Pablo Martinez Monsivais, Associated Press
In this Dec. 9, 2009, file photo, Sen. Mary Landrieu, D-La., speaks at a health care news conference on Capitol Hill in Washington.

Democratic Louisiana Sen. Mary Landrieu said Friday that her campaign has reimbursed the federal government $33,727 for flights she took that included political fundraising events dating back to February 2002.

"I take full responsibility. They should have never happened, and I apologize for this," Landrieu said in a news release. "A new system has been established that has been successfully used by a number of Senate offices to provide a safeguard from this happening in the future."

Landrieu is seeking a fourth term in November, and is considered one of the most vulnerable Senate incumbents this year.

Louisiana Republican Party director Jason Dore filed a complaint Sept. 2 with the Senate Ethics Committee, accusing Landrieu of billing taxpayers for campaign travel.

In February 2002, rules changed about flights that include both official business and campaign activities. If political events make up at least 15 percent of the time for a senator's trip, the campaign must pay a prorated share of the flight cost. Before then, costs were fully paid either by the government or the campaign.

Hours before Landrieu released her statement Friday, the Republican National Committee's communications director, Sean Spicer, issued a memo questioning specific charter flights Landrieu had taken from 2000 to 2008. Spicer said the trips coincided with some donations listed on Landrieu's campaign finance reports.

A campaign spokesman for Republican U.S. Rep. Bill Cassidy, who's trying to unseat Landrieu, criticized the senator for not releasing information about payments for private flights she took during her first term, starting in 1997.

"Sen. Landrieu cites a rule change in 2002, but prior to that, it was also illegal to bill taxpayers for private flights," Cassidy campaign spokesman John Cummins said in a news release. "Given Senator Landrieu's own admission of faulty oversight, how do taxpayers know that problems did not exist prior to 2002?"

Rob Maness, a tea party-backed Republican who's also running for Senate in Louisiana, said Washington politicians "live in a complete alternate universe from the rest of us."

"What's disturbing is that if Sen. Landrieu hadn't been caught, the illegal use of taxpayer dollars for political travel would have likely continued for as long as she was in office," Maness said in a news release. "Is it any wonder why so many people have lost faith in their government?"