About 20 women were brought to the hotel in Colombia where Secret Service agents were accused of inviting prostitutes back to their rooms, a US lawmaker said Tuesday after being briefed on the widening scandal.

The security breach ahead of last weekend's Summit of the Americas attended by President Barack Obama is "potentially extremely serious," Senator Susan Collins, ranking Republican on the Homeland Security and Governmental Affairs Committee, said after being briefed by Secret Service director Mark Sullivan.

"He told me that there are 11 Secret Service agents and officers involved," she said in a statement.

"Some 20 women foreign nationals were brought to the hotel in (Colombia), but allegedly marines were involved with the rest."

She later told reporters that some of the agents involved "were uniformed personnel who are assigned to building security. Others were these specialized agents who do security details."

A spokesman for US President Barack Obama said he still has "confidence" in Secret Service Director Mark Sullivan, despite the widening sex scandal clouding the elite protection division, his spokesman said Tuesday.

"The president has confidence in the director of the Secret Service," White House spokesman Jay Carney said, responding to the latest allegations surrounding alleged misconduct by agents involving prostitutes in Colombia.

Collins said Sullivan was "absolutely appalled" by the actions of the Secret Service personnel involved and is pursuing a vigorous internal investigation.

He told her that all agents involved "have been interviewed," the senator said.

"If the fact is proved to be as reported on this, this is an incredible lack of character and breach of security and potentially extremely serious," she said echoing the statements of other officials that the incident was not just an embarrassment, but a security risk.

"We don't know who these women are. They could be spies, they could be associated with hostile forces, they could have disabled the agents weapons, or planted listening devices," she said.

The Pentagon said earlier that more than five US military personnel were also being investigated over alleged misconduct in the resort of Cartagena, the summit's host city.

The US source said on condition of anonymity that the agents, who have been placed on administrative leave, had their security clearances suspended pending an investigation into the allegations.

Collins said she put several questions to Sullivan, including whether the women "jeopardized security of the president or our country."

She said she also wanted to know, "given the number of personnel involved, does this indicate a problem with the culture of the Secret Service?"

Obama said on Sunday that he expected a "rigorous" investigation into the scandal, warning he would be "angry" if the claims -- reportedly also involving a dispute over payment to a prostitute -- were proven true.

The military is conducting a separate probe and has confined the service members involved to their barracks.

None of the Secret Service personnel involved -- both agents and uniformed officers -- was assigned to Obama's personal security detail.

The personnel were from more than one branch of the military, and some of them were at the same hotel as Secret Service agents alleged to have brought prostitutes to their rooms, a Pentagon spokesman said earlier.