The Obama administration is urging Egypt to "immediately" lift travel restrictions on several U.S. citizens, after the son of Transportation Secretary Ray LaHood and other Americans were prevented from leaving the country.
The travel restrictions stem from a raid last month on nongovernmental organizations, or NGOs. U.S. officials have protested the treatment of those groups, including three U.S.-based groups, but the situation escalated when it emerged that the Egyptian government has created what was described as a "no-exit list."
State Department spokeswoman Victoria Nuland said top officials -- including Secretary of State Hillary Clinton -- have gotten involved. She said the administration so far knows of "four or five specific cases" where Americans have tried to leave and "had difficulties."
"We are urging the government of Egypt to lift these restrictions immediately and allow folks to come home as soon as possible," she said, later adding: "Frankly, we don't know how this is going to come out yet."
Though the individuals stuck in Egypt have not technically been detained, those whose NGOs have been targeted say they continue to be concerned that arrest warrants could be issued.
Sam LaHood, the son of the U.S. transportation secretary, runs the Egypt program for the International Republican Institute and has been prevented from leaving the country. "Anything is possible at this point," he said, when asked whether the investigation could lead to arrests.
LaHood, in an email to Fox News, said three Americans with the International Republican Institute are on the no-exit list, as well as two other non-Americans.
"We understand that the issue is being raised at high levels between our governments, but we have no information that this is close to any conclusion," he said.
LaHood also detailed what happened when he tried to leave on Saturday. He said he was stopped by a security officer while trying to pass through the passport check at the Cairo airport.
"He pulled me out of line and asked me to wait. After an hour a (woman) from the Immigration Department emerged with my passport and told me I was denied exit from Egypt," he wrote. "I asked her why, and she told me she did not now. I asked what the problem was, and she said she did not know. I asked what I needed to do to fix the issue, and she said she did not know.
"After another 45 minutes a man arrived with my passport and he escorted me out of the terminal and to the street."
The IRI later found out about the no-exit list.
Nuland said Clinton spoke to Egypt's foreign minister over the weekend, and she added that the U.S. ambassador to Egypt is also "very involved."
Meanwhile, Secretary LaHood said Thursday that he has been in contact with his son.
"I'm very gratified by all the work that's going on by the administration and our ambassador in Egypt, and so I appreciate the work they're doing on that," he said.
Arizona Republican Sen. John McCain, who is chairman of the IRI board, on Thursday called on Egypt to lift the travel restrictions on LaHood and other NGO workers.
"It is outrageous that these individuals would be held against their will by Egyptian authorities and prohibited from leaving the country," he said in a statement. "I deeply regret that this crisis has escalated to the point that it now endangers the lives of American citizens and could set back the long-standing partnership between the United States and Egypt."
In the raids, the Egyptian government confiscated equipment and closed offices at several of the sites. The groups were accused of operating without proper registration and using foreign funding, said Scott Mastic, director of IRI's Middle East division. But he decried the raids as politically motivated and not "reflective of a legal process."
Given the existence of the no-exit list, he said the groups are concerned about "further escalation."
Mastic said late Wednesday that his organization has been told the no-exit list would be lifted, but he expressed doubt -- given that prior assurances that the Egyptian government would return confiscated materials so far have not been honored.
"Frankly, at this point, we don't have a lot of faith that that will happen in short order, because there's just not been any signs of positive progress since the initial raids," he said.
Fox News' Catherine Herridge and FoxNews.com's Judson Berger contributed to this report.