(CNN) -- Sen. Barack Obama called for an investigation Friday into how the security of the passport files of the three remaining presidential candidates was breached.
The State Department admitted Friday that the passport files of Obama, Sen. Hillary Clinton and Sen. John McCain had been accessed without authorization.
"One of the things that the American people count on in their interactions with any level of government is that if they have to disclose personal information, that it stay personal and stay private," Obama said in Portland, Oregon.
"And when you have not just one but a series of attempts to tap into people's personal records, that's a problem not just for me but for how our government is functioning," he said. Watch Obama call for an investigation »
Obama said he expected "a full and thorough investigation" by the administration in conjunction with congressional oversight committees.
The State Department's inspector general has started an investigation, department officials said.
Attorney General Michael Mukasey said the Justice Department had not launched an investigation and did not expect to do so unless it was asked by the inspector general.
State Department spokesman Sean McCormack said Obama's files had been viewed three times by contractors working for the agency starting in January.
The department hires contractors to design, build and maintain their systems and help employees with searches.
One of the contractors who viewed Obama's file also looked at the file of McCain, the probable Republican presidential nominee.
Two contractors were fired and a third disciplined after they accessed Obama's file, McCormack said.
"We are reviewing our options with that person and his employment status," McCormack said. Watch McCormack's explanation »
In Clinton's case, a trainee accessed her files in 2007.
McCormack said two of the contractors in the Obama case were "low-level" personnel and the other was in a mid-level position with no management role.
McCormack said senior management at the State Department was not aware of the incidents until Thursday afternoon. The breaches involving Obama's file occurred January 9, February 21 and March 14.
McCormack said Secretary of State Condoleezza Rice apologized to Clinton and Obama and would soon speak to McCain, who is traveling in Europe. Watch Rice apologize for the breach »
"If anyone's privacy was breached, then they deserve an apology and a full investigation, and I believe that will take place," McCain said in Paris Friday.
Rice said she told Obama the State Department inspector general would launch an investigation.
"I told him I was sorry, and I told him that I myself would be very disturbed if anyone had looked at my passport files and that, therefore, I will stay on top of this," Rice said.
Rice said "it appears that the system worked" because the unauthorized viewing was flagged, but "it should have been known to senior management."
State Department officials said the contractor companies are The Analysis Corporation and Stanley Inc. The latter has had contracts with the department since 1992 and was recently awarded a $570 million contract to provide support for passport processing.
Stanley Inc. officials confirmed that two of its employees had unauthorized access to Obama passport files. Both individuals were fired, according to a company statement Friday. "While this is a rare occurrence, we regret the unauthorized access of any individual's private information," the statement said.
The Analysis Corp., also in a statement Friday, confirmed that one of the contractors involved in the breach was a company employee and called it "an isolated incident."
"This individual's actions were taken without the knowledge or direction of anyone at The Analysis Corp. and are wholly inconsistent with our professional and ethical standards," the statement on the company's Web site said.
The company, which has contracted with the U.S. government for nearly 20 years, said it would fully cooperate with the federal investigation.
A State Department source said passport files contain scanned images of passport applications, birth date and basic biographical information, records of passport renewal and possibly citizenship information.
The White House said Rice briefed President Bush about the security breach involving Obama's files at 7 a.m. Friday.
Undersecretary of State Pat Kennedy briefed the staff of the three senators Friday.
"We at the State Department have very, very rigorous rules about controls and access for privacy materials, and we review them regularly. When you have a large organization with a lot of people in it, mistakes and errors happen from time to time, but that's why we stepped in and we caught these," Kennedy said after the meeting. E-mail to a friend
CNN's Zain Verjee, Jessica Yellin, Terry Frieden and Ted Barrett contributed to this report.