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A woman at the centre of the US prostitution scandal in Colombia asked for $800 (£500) to spend the night with a US agent, the New York Times reports.

The woman - who describes herself as an escort, not a prostitute - the agent reneged on their deal, instead offering only $30.

That sparked a row that blew the lid off a night that saw 20 women taken back to the hotel in Cartagena.

Three Secret Service staff are leaving the agency in the wake of the incident.

One supervisor was sacked, one retired and a more junior employee resigned, the agency's assistant director said on Tuesday.

The wild night in Cartagena's Hotel Caribe saw a group of 11 Secret Service agents sent home from Colombia ahead of President Barack Obama's visit to the city for last weekend's Summit of the Americas.

As many as 12 military personnel are also said to have been involved and are also under investigation.

The woman's account of the night at the Pley Club, described as a high-end strip club in an industrial part of Cartagena, sheds more light on the events that led to the public outing of the military and Secret Service personnel.

According to the prostitute's account, the Americans bought bottles of vodka to share with a group of women they approached in the club.

"They never told me they were with Obama," she told the newspaper, adding: "They were very discreet."

In an interview with the New York Times, the unnamed woman said the US agent had agreed a price of $800 for a night with her.

But he changed his mind in the morning, she said, offering just $30 and sparking a furious row that ended with police being asked to intervene.

She told the Times she did not describe herself as a prostitute, suggesting that her price indicated she was a high-end escort.

"It's the same, but it's different. It's like when you buy a fine rum or a BlackBerry or an iPhone. They have a different price."

The woman said she was now scared of the implications of what had happened and planned to leave the city in the coming days.

"This is something really big. This is the government of the United States."

Senator Susan Collins, who has been briefed regularly on the official investigation into the incident, told the New York Times that the woman's account seemed to tally with her understanding of what happened in Cartagena.

Representative Peter King, who sits on the House Homeland Security Committee, added that some of the men may not have known the women were prostitutes.

"I understand there was quite a bit of drinking going on," he told the newspaper.

Senior US officials say 20 women were found at the Cartagena hotel before President Obama went to the Summit of Americas last weekend.

Lie detector tests are being used on the accused as investigations into the scandal continue.

"We demand that all of our employees adhere to the highest professional and ethical standards and are committed to a full review of this matter," Secret Service Assistant Director Paul Morrissey said in a statement.

He said inquiries were at an early stage, and another eight officers were still being investigated.

The three agents stepping down have been placed on administrative leave and their security clearance had been revoked. They were not directly involved with presidential security.

The two supervisors leaving the Secret Service are both said to have more than 20 years experience.

Senator Collins said after a briefing by the head of the Secret Service Mark Sullivan that she was "rightly appalled by the agents' actions".

She has raised concerns over potential breaches of security, including whether the women could have placed bugs on the men.

A Marine Corps spokesman said on Tuesday that among the military service members being investigated were two Marine dog handlers assigned to support the Secret Service.

The White House meanwhile said it had confidence in the director of the Secret Service to investigate the incident.