Those six work for the International Republican Institute and the National Democratic Institute, two democracy-building groups with close ties to United States Congressional leaders. The groups are under a criminal investigation by the Egyptian authorities over allegations that they violated rules on foreign funding.

It was unclear how many of the Americans had sought refuge in the embassy. One source, speaking on the condition of anonymity, said there were three, all from the International Republican Institute, who had become concerned because of news reports that the investigation was nearly completed and that they might be arrested. It was also unclear what would happen if the Egyptian authorities pressed charges, since the sheltered Americans do not have diplomatic immunity.

The dispute over the activity of the groups and the status of their employees comes as American officials stepped up their public calls for the military council to hand over power to civilians as soon as possible, as it had promised when it took over with the ouster of President Hosni Mubarak last year.

The military-led interim government, meanwhile, has often suggested that the United States was financing nonprofit groups that it alleged were behind protests meant to destabilize Egypt or bring down the state. Generals on the ruling military council have said the investigation of the American-backed nonprofit groups will shed light on the origins of those protests.