Egypt has blocked workers at two U.S.-funded advocacy groups from leaving the country as part of an investigation of the organizations that has raised tensions between Cairo and Washington, says The New York Times.

Sam LaHood, Egypt director for the International Republican Institute and the son of U.S. Transportation Secretary Ray LaHood, was briefly detained at the Cairo airport Saturday before being allowed to board a flight to Dubai.

Egypt’s military government said Thursday that six Americans working for Mr. LaHood’s group or its sister organization, the National Democratic Institute, had been barred from leaving the country. Egypt is investigating alleged interference in domestic political affairs by foreign groups, several of which were raided by police and soldiers late last month. Mr. LaHood said his organization is cooperating with the inquiry by Cairo judges.

The Obama administration has warned Egypt that continued American military aid hinges on tangible steps toward democracy in that country, where a military government has ruled since President Hosni Mubarak was deposed last year. Both the previous and current regimes have blamed unrest in the country on outside democracy-building groups.