The US military said Friday it is now investigating 11 service members linked to the growing sex scandal in Colombia that has rocked the president's Secret Service.

The Pentagon had initially said five troops were implicated and later said there were 10 suspects.

"I can tell you now, based on an update by the investigating officer (IO) to the commander of SOUTHCOM (Southern Command), the number of US service members being considered by our investigating officer is 11," Colonel Scot Malcom said an email to reporters.

There were six suspects from the US Army's 7th Special Forces Group, two from the Marine Corps, two from the Navy and one from the Air Force, said Malcom, a spokesman for US Southern Command, which oversees forces in Central and South America.

As the investigation was still underway, the spokesman could not say why another suspect had emerged.

An Air Force colonel in charge of the investigation flew to Colombia on Monday to gather facts in the case and was due return to the United States probably over the weekend. He then will interview the suspects in the case, Malcom said.

The military suspects, all enlisted personnel, were helping with preparations for President Barack Obama's visit to Cartagena for the Summit of the Americas last weekend.

Eleven Secret Service agents and the military service members are accused of consorting with prostitutes at a hotel.

About 20 prostitutes were allegedly brought to the hotel, according to an account from Senator Susan Collins, who was briefed by the Secret Service.

Lawmakers say the incident raised serious questions about security and the work of the Secret Service, the president's elite protection squad.

[Photo of the hotel in Colombia that has rocked the president's Secret Service via AFP/Manuel Pedraza]