The United States on Thursday urged Egypt to lift travel bans placed on several U.S. pro-democracy activists in connection with a crack down on non-governmental organizations (NGOs) that has strained ties between Washington and Cairo.

We are urging the government of Egypt to lift these restrictions immediately and allow these folks to come home as soon as possible, State Department spokeswoman Victoria Nuland told a news briefing.

She said the United States was aware of four or five cases of U.S. citizens who had been prevented from leaving Egypt, but said they still had their passports and were not being physically detained.

Among those targeted by the travel ban is Sam LaHood, the Egypt director of the International Republican Institute and son of U.S. Secretary of Transportation Ray LaHood, officials at the non-governmental organizations said.

The United States, which gives $1.3 billion (828.5 million pound) a year in aid to Egypt's military, reacted sharply when the Egyptian authorities swooped in on some 17 NGOs in December. It had hinted that the military aid could be reviewed if the raids continued.

(Reporting By Andrew Quinn; Editing by Will Dunham and Sandra Maler)