Updated 11:15 a.m. ET
(CBS News) Senator Charles Grassley, the top Republican on the Senate Judiciary Committee, sent a letter to the head of the Secret Service Friday evening asking if White House staff are also subjects of the investigation into the Colombian prostitution scandal.
Grassley is questioning the "possible involvement of staff from the White House Communications Agency and the White House Office of Advance," spokesperson Beth Levine wrote in a statement.
Grassley, whose committee has oversight of the Secret Service, sent the letter to Director Mark Sullivan and Department of Homeland Security Inspector General Charles Edwards on Friday evening after his staff received the latest briefing on the incident.
In his letter, Grassley asked for questions to be answered, including whether the Secret Service reserved or shared rooms at Hotel Caribe (the hotel in Cartagena, Colombia where Secret Service personnel were staying) for staff members of the White House Communications Agency or the White House Office of Advance. If so, Grassley asked if the log of visiting guests was obtained and examined - and if not, why not?
"It is my understanding that ordinarily the Secret Service advance team works closely with the White House Communications Agency," Grassley wrote.
White House spokesperson Jay Carney told reporters Friday that he's not aware of any White House staff involved in the investigation.
"I have no reason to believe -- I do not know otherwise that this did not involve anything but the agents and the military personnel," Carney said.
The White House Communications Agency is under the White House Military Office and handles secure and non-secure communications - including telephone calls - for the president and vice president.
The White House Office of Advance coordinates logistics and travel itineraries for the White House and the traveling press corp.
Although Senator Grassley praised the swiftness of the investigation by the Secret Service Office of Professional Responsibility so far, he said the investigation must continue.
"More work remains to investigate and uncover what occurred, hold those responsible accountable, and to put in place new policies and procedures to prevent future misconduct," Grassley wrote.