WASHINGTON - The White House said on Monday that an Egyptian crackdown on pro-democracy non-governmental groups that has enmeshed a number of US citizens could threaten the country's $1.3 billion in annual US military aid.Nineteen Americans are among 40 foreign and Egyptian activists whose cases have been referred to criminal court by the country's army-backed government. A number of the US citizens involved have sought refuge in the American embassy. "These actions could have consequences for our relationship and for our assistance programs," White House press secretary Jay Carney told reporters.The row has strained ties between Cairo and Washington, which backed the overthrow last year of Egypt's longtime ruler Hosni Mubarak, upon whom it relied for decades to uphold a peace treaty with Israel vital to US strategy in the Middle East."We continue to communicate at all levels with the Egyptian government our grave concerns regarding the crackdown against NGOs," Carney told a news briefing, adding that the individuals "have done nothing wrong. Their only assignment is to support Egypt in its transition to democracy."Egyptian authorities say the NGOs broke the law by accepting foreign funds without government approval.Several US citizens and others involved in the probe have been barred from leaving Egypt. They include Sam LaHood, the country director of the International Republican Institute (IRI) and the son of US Transportation Secretary Ray LaHood."Many of these groups have worked in Egypt for several years, and so their activities are not new. Moreover, they also served as observers for the recent parliamentary elections at the request of the government of Egypt," Carney said.