Hoboken Mayor Dawn Zimmer's weekend switch from Chris Christie booster to Christie accuser has drawn a sharply worded denial of her charge that the governor's office withheld Sandy aid from her city because she balked at fast-tracking a commercial development project.

Mayor Dawn Zimmer (L) of Hoboken chats with New Jersey Governor Chris Christie (R) prior to a joint press conference on November 4, 2012 in Hoboken (Andrew Burton/Getty Images)

Zimmer, a Democrat whose effusive praise of Republican Christie last August read like a quasi-endorsement of his re-election bid, now says Lt. Gov. Kim Guadagno pulled her aside at a supermarket opening last May and told her unless the development project was approved "we are not going to be able to help you."

Guadagno challenged Zimmer's story Monday, saying she "wholeheartedly denied" the allegation.

Christie spokesmen also hit back hard on Sunday, accusing Zimmer of trying to benefit from the unfolding Bridgegate investigations -- a suggestion echoed by unsuccessful Democratic gubernatorial candidate Barbara Buono on Sunday.

Zimmer, speaking to to MSNBC and The Associated Press Saturday, said Guadagno told her Sandy recovery funds would not flow to her flood-damaged city unless a commercial development favored by the Christie administration went forward. MSNBC reported that the project was being handled by the law firm of Port Authority chairman David Samson, a Christie confidant whose name has surfaced in subpoenaed Bridgegate documents.

Late Sunday, Politico was reporting that Zimmer had met with the U.S. Attorney's office in New Jersey about her allegations, supplying them with documents and a journal she said she kept during through the episode.

Zimmer, in the MSNBC interview, said Guadagno also told her the ultimatum came directly from Christie and added:: "'I know it's not right, I know these things should not be connected, but they are and if you tell anyone I'll deny it.'"

Guadagno Monday said, "Mayor Zimmer's version of our conversation in May of 2013 is not only false but is illogical and does not withstand scrutiny when all of the facts are examined. Any suggestion that Sandy funds were tied to the approval of any project in New Jersey is completely false."

Christie's office, calling Zimmer's charges "outlandishly" and "categorically" false Sunday, issued a statement pointing to the "public praise" she had given the governor last year for his handling of New Jersey's Sandy recovery.

"The Governor and Mayor Zimmer have had a productive relationship, with Mayor Zimmer even recently saying she's 'very glad' he's been our Governor," the statement said. "It's very clear partisan politics are at play here as Democratic mayors with a political axe to grind come out of the woodwork and try to get their faces on television."

In one Aug. 20 tweet cited by Christie's office, Zimmer appeared to suggest she would be joining other Democratic mayors in endorsing the governor for re-election but for Hoboken's own non-partisan municipal elections. She tweeted:

"To be clear I am very glad Governor Christie has been our Gov. I am not endorsing bc of Hob's non-partisan mayoral race."

A lengthy denial issued by Christie's office stated Hoboken is slated to receive at least $70-million of some $300-million in Sandy aid that was intended to be shared with other New Jersey localities. Zimmer Saturday told MSNBC that her city received only $342,000 of the $127 million she had requested.

[Full text of Christie Administration Response to Zimmer's MSNBC interview]

Buono tweeted Sunday morning with an indirect reference to the Bridgegate investigations into charges George Washington Bridge lane closings in September were aimed at punishing a Democratic mayor for not endorsing Christie. Buono, whose own doomed candidacy drew little support from Democratic mayors, tweeted:

“Good @dawnzimmernj came forward but question is: why did she wait until she smelled blood in the water?”

Zimmer, offering to take a lie-detector test, said she didn't reveal the conversation until this weekend because she feared no one would believe her. A week earlier, she told WNYC radio that Christie was disappointed she did not endorse him for re-election. However, she made no mention in that interview of his administration using Sandy aid to pressure her for support of the redevelopment project.

Assemb. John Wisniewski (D-Middlesex), chairman of the state legislature's special Bridgegate committee, told NBC's Meet the Press Sunday that Zimmer's allegations should be taken seriously and would be looked into by the committee.

Wisniewski was himself the target of an attack by Republican Rudy Giuliani in a separate Meet the Press segment Sunday. The former New York City Mayor said the New Jersey assemblyman should recuse himself from the investigation because his public statements indicate he has prejudged the outcome by saying he does not believe Gov. Christie's denials of involvement in the bridge closings.

"It clearly is a partisan witch hunt," Giuliani said of Bridgegate.

In response, a spokesman for Assembly Democrats said, "Rudy Giuliani quite simply has no idea what he's talking about. Chairman Wisniewski has been praised by Republicans for his work and Republicans unanimously voted with Democrats to continue the investigation into what happened with this threat to public safety and abuse of government power."

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The Associated Press and Dan Alexander contributed to this report.