CAIRO: Egypt said on Wednesday it would not be swayed by threats to aid when investigating foreign-funded pro-democracy groups and NGOs, a case that has prompted Washington to warn that U.S. military support worth $1.3 billion a year may be in jeopardy.

The United States wants Egypt to drop travel bans on at least 19 U.S. citizens involved in the case but Egypt's government says it cannot intervene in a judicial probe of non-governmental organisations (NGOs) over whether they violated laws such as receiving foreign cash without official approval.

A total of 43 foreign and local activists are banned from leaving Egypt and their case has been referred to a criminal court.

"Egypt will apply the law ... in the case of NGOs and will not back down because of aid or other reasons," army-appointed Prime Minister Kamal al-Ganzouri told a news conference.

The case has put a deep strain on relations with Washington, which counted Egypt as a close strategic ally under ousted President Hosni Mubarak. Both U.S. Congress and the White House have warned that the crackdown could threaten the aid budget.

Two Egyptian officials told Reuters on Tuesday that the government would back down because allowing the row to drag on could jeopardise aid from Washington that began flowing after Egypt in 1979 became the first Arab state to make peace with Israel.

The row adds to tensions over an uncertain transition to democracy under an army council which took charge after Mubarak was driven from office by a popular uprising on Feb. 11. Egypt is still reeling from political turmoil and violence.

Some of the U.S. citizens, belonging to the U.S.-funded National Democratic Institute (NDI) and International Republican Institute (IRI), which have loose links to the top U.S. political parties, sought refuge in the American embassy.

U.S. officials have not said how many.

Judge Sameh Abu Zaid, one of two judges leading the probe, told a separate news conference on Wednesday that the raids on NGO offices at the end of last month, and which first drew U.S. criticism, were conducted in line with Egyptian criminal law.

He said a travel ban was imposed when some called for questioning left the country. Lawyers produced travel documents as proof of absence. "In such situations, the judges place a travel ban to be able to continue the investigation," Abu Zaid said.

"There is a lot of evidence, some of it dangerous. We have about 160 pages of evidence," the judge said.

He said one foreign NGO had sought help from a local operation to launch an online page to list the number and locations of churches, as well as identify the location of army units in Ismailia and Suez, cities east of Cairo. He said this indicated political activities outside the mandate of NGOs.