CAIRO — Egypt banned at least 10 Americans and Europeans from leaving the country, including the son of U.S. Transportation Secretary Ray Lahood, hiking tensions with Washington over a campaign by Egypt’s military against groups promoting democracy and human rights.

The United States warned Thursday that the campaign raised concerns about Egypt’s transition to democracy and could jeopardize American aid that Egypt’s battered economy needs badly after a year of unrest.

The travel ban was part of an Egyptian criminal investigation into foreign-funded democracy organizations after soldiers raided the offices of 10 such groups last month, including those of two American groups.

The investigation is closely intertwined with Egypt’s political turmoil since the fall of Hosni Mubarak nearly a year ago. The generals who took power have accused “foreign hands” of being behind protests against their rule and they frequently depict the protesters themselves as receiving foreign funds in a plot to destabilize the country.

Egyptian opponents of the military say the generals are trying to smear the protesters in the eyes of the public and silence organizations they fear will undermine their managing of the country.

Also startling is the military’s willingness to clash with its longtime top ally, the United States, over the issue, particularly since the army itself receives more than $1 billion a year from Washington. The December raids brought sharp U.S. criticism, and last week President Barack Obama spoke by telephone with Egyptian military chief Field Marshal Hussein Tantawi to emphasize “the role that these organizations can play in civil society,” according to State Department spokeswoman Victoria Nuland on Thursday.

The ban became public after Sam LaHood, Egypt director of the Washington-based International Republican Institute, went to Cairo’s airport Saturday to catch a flight and was told by an immigration official that he couldn’t leave.

“I asked her why I was denied, she said she didn’t know. I asked how to fix it, and she said she didn’t know,” said LaHood, 36. An hour later, a man in civilian clothes gave him back his passport and escorted him to the curb, LaHood said.

“It’s a dark signal for groups who are interested in doing this kind of work,” he said.

LaHood’s father, a former congressman from Illinois, is the only Republican in Obama’s Cabinet. The elder LaHood declined to comment.

The IRI was among the groups raided last month, along with the National Democratic Institute and a number of Egyptian organizations. Both American groups, linked to the political parties of the same name, monitored Egypt’s recent parliamentary elections. In the raids, troops ransacked 17 offices of the 10 organizations around the country, carting away computers and documents.

The Egyptian government said the raids were part of a legitimate investigation into whether the groups were operating legally.

Sen. John McCain blasted Egypt’s handling of the issue Thursday, warning that continued restrictions on civil society groups “could set back the long-standing partnership between the United States and Egypt.”

IRI and NDI officials said they have been trying since 2005 to register as required by law, but were left in legal limbo, never officially denied nor granted permission. Both groups continued to operate while keeping authorities abreast of their activities, they said. Many Egyptian non-governmental organizations say officials often keep their groups in such limbo to maintain a threat over their heads.

Sam LaHood said he was told by his lawyer that he is under investigation on suspicion of managing an unregistered NGO and receiving “funds” from an unregistered NGO, namely, his salary.

Two other Americans and a European with IRI have also been banned from travel, Lahood said his lawyer had been told. From the National Democratic Institute, three Americans and three Serb employees are also on the list, according to its Egypt director Lisa Hughes.

Hughes, who is among those barred, said she has been interrogated for more than four hours about her group’s work and that she had planned to fly to the U.S. next month before she heard about the ban.

“I think we would be silly not to be concerned,” she said. “We were concerned the moment armed men showed up at our office door, and this has done nothing to calm those concerns.”

The State Department’s top human rights official, Michael Posner, told reporters in Cairo Thursday that such moves could jeopardize U.S. aid to Egypt, one of the biggest recipients.

“All need to have the ability to operate openly, freely, without constraint, not based on the content of their work,” he said.

Posner pointed to recent U.S. legislation that blocks annual aid to Egypt unless it takes certain steps. These include abiding by its 1979 peace treaty with Israel, holding free and fair elections and “implementing policies to protect freedom of expression, association and religion and due process of law.”

“Obviously, any action that creates tension between our governments makes the whole package more difficult,” Posner said.

The U.S. is due to give $1.3 billion in military assistance and $250 million in economic aid to Egypt in 2012. Washington has given Egypt an average of $2 billion in economic and military aid a year since 1979, according to the Congressional Research Service.

Egypt’s military has been locked in a confrontation for months with protesters who demand it immediately hand over power to civilians.

Hundreds of protesters camped Thursday in Cairo’s central Tahrir Square, a day after several hundred thousand people massed there to mark the one-year anniversary of the 18-day anti-Mubarak uprising.

Thursday evening, hundreds moved from Tahrir and rallied in front of the state TV building, beating drums as they chanted for the “liberation” of state-run media from the military’s control. They projected video footage of soldiers beating protesters onto the building.

State TV has been a mouthpiece of the military, broadcasting its accusations against protesters. Activists demand it be restructured as an independent media institution.

“The media is still manipulated and projects the same lies,” said protester Mahmoud Ragab. “We will be here everyday to let them know it is a revolution.”

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Associated Press writer Sarah El Deeb contributed to this report.