WASHINGTON - The United States has begun to take disciplinary action against its secret service agents involved in the prostitution scandal in Columbia, with three agents from an advance team for President Barack Obama’s weekend trip being forced out.

The exit on Thursday of two supervisors and a lower ranked employee from the agency given the prime job of protecting the US President is just the start, according to media reports. One of the key questions now is how high the accountability will go.

Secret Service director Mark Sullivan, who served on the presidential protection detail for Bill Clinton, is considered safe for now. But his job could be in jeopardy if it turns out the caper in the Colombian city of Cartagena ahead of Obama’s arrival was part of a pattern of behaviour under his nose, the reports said. The Secret Service is investigating 11 agents for alleged misconduct after a night of partying ended in prostitutes coming back to their Cartagena hotel. A further 10 US military personnel are also under investigation - at this point for breaking their curfew - in an imbroglio reportedly involving up to 20 women.

The call-girl scandal, rated one of the biggest in the history of the Secret Service, embarrassed Obama at the weekend, overshadowing his Colombian visit to meet 30 leaders at the Summit of the Americas.

Despite the President’s attempts to keep his message focused on free trade and combating illicit drug smuggling, news reports and the conference chatter were all about the bad behaviour of Secret Service agents. The Secret Service confirmed that one supervisor in the advance team sent to Colombia to check security arrangements for Obama’s visit had been allowed to retire.

Another supervisor was to be sacked and an agent had resigned in the midst of an aggressive investigation involving lie-detector tests and interviews with staff at Cartagena’s Hotel Caribe.

Peter King, a Republican congressman and chairman of the Homeland Security Committee in the US House of Representatives, said yesterday the Secret Service had taken action against three people where the case was believed to be clearest. “It’s certainly not over,” he said.

As well as a rigorous investigation promised by Sullivan, King has launched his own probe in order to get to the bottom of the affair.

Darrell Issa, a Republican who heads the House committee on Oversight and Government Reform, sent a letter to Sullivan asking for a detailed description of the misconduct, how many personnel were involved and who knew about it.

In his letter, Issa said allegations involving so many Secret Service personnel in Cartagena “raised questions about the agency’s culture”.

Susan Collins, the leading Republican on the US Senate’s Homeland Security Committee, was also sceptical about the Cartagena incident being a one-off. “Think of all the missions and countries that the Secret Service visits in advance of the President’s trips,” she said.

The main worry for Washington’s political establishment is that the President’s security could have been at risk if contact with unknown women in Colombia exposed agents to blackmail or if they willingly gave away confidential information about Obama’s schedule, according to repoorts.

The scandal erupted after one woman stayed in an agent’s room past a morning curfew allowed for female guests by hotel management. The agent refused to open his door to the hotel’s manager, prompting the involvement of local police. An argument ensued after the agent refused to pay the woman money she had demanded.