Updated

An Egyptian court has adjourned the trial of 16 Americans and 27 other employees of nonprofit groups until April 26.

Judge Mahmoud Mohammed Shoukry presided over a chaotic opening session of the trial Sunday before adjourning the case until the end of April.

The NGO workers have been charged with operating without a license and using illegal foreign funds to foment unrest.

Thirteen Egyptian defendants were in court for the opening hearing. They were held in a metal cage, as is customary in Egyptian trials.

Of the 16 Americans charged in the case, seven have been banned from leaving Egypt. They were not in court Sunday.

The case has severely strained U.S.-Egyptian relations. American officials have threatened to cut off $1.5 billion in aid if the dispute is not resolved.

The case, which involves American employees of four U.S.-based pro-democracy groups, has tested one of Washington's most pivotal relationships in the Middle East, and prompted U.S. officials to threaten to cut a $1.5 billion annual aid package to Egypt if the issue is not resolved.

Egyptian authorities have responded by blasting what they call U.S. meddling in Egypt's legal affairs.

There are 43 defendants in the case -- 16 Americans, 16 Egyptians, as well as Germans, Palestinians, Serbs and Jordanians. They have been charged with the illegal use foreign funds to foment unrest and operating without a license. But the investigation fits into a broader campaign by Egypt's rulers against alleged foreign influence since the ouster of longtime rule Hosni Mubarak last year.

Rights groups have sharply criticized the investigation into the pro-democracy groups and the charges, saying they are part of an orchestrated effort by Egyptian authorities to silence critics and cripple civil society groups critical of the military's handling of the country's transition to democracy. Egyptian officials counter by saying the trial has nothing to do with the government and is in the judiciary's hands.

President Barack Obama has urged Egypt's military rulers to drop the investigation, and high-level officials, including Joint Chiefs Chairman Martin Dempsey and Republican Sen. John McCain, have flown in to Cairo to seek a solution.

A senior U.S. official said Saturday the Obama administration is in "intense discussions" with Egypt to resolve the legal case "in the coming days."

The official, speaking to reporters on condition of anonymity due to the delicacy of the matter, said that Secretary of State Hillary Rodham Clinton had raised the matter twice in person with Egypt's foreign minister -- once in London and once in Tunisia -- in the past three days and that other senior U.S. officials are actively involved.

However, the U.S. cannot be seen as pushing too hard against Egypt's ruling military council, which is viewed as the best hope for a stable transition for a nation that is not just a regional heavyweight, but also the most populous in the Arab world and a lynchpin in Washington's Middle East policy, largely because of its landmark peace treaty with Israel.

The U.S. State Department says that seven of the 16 Americans facing trial have been barred from leaving Egypt by the country's attorney general. Several Americans, including Sam LaHood, son of Transportation Secretary Ray LaHood, have sought refuge in the U.S. Embassy.

The Americans work for four U.S.-based groups: the International Republican Institute, the National Democratic Institute, Freedom House and a group that trains journalists.

The dispute began in December when Egyptian security forces raided the offices of the pro-democracy groups, seizing documents and computers.

Earlier this month the NDI said in a statement that it denies the accusations and that it fulfilled all of the registration requirements for the past six years, including a number of updates provided in January.

Freedom House President David J. Kramer said this month that the charges against the NGOs indicates that freedom in Egypt "has only gotten worse" under Mubarak's appointed ruling generals who took power after the longtime authoritarian leader was toppled.

"Let me state clearly that we do not view this situation as a legal matter involving rule of law," Kramer said. "The charges are clearly political in nature and without foundation."

The state-run al-Ahram daily on Sunday reported that 19 Americans, not 16, were facing trial.

The newspaper, quoting leaked Egyptian intelligence reports, said that some of the computers seized in the raid had sensitive information affecting Egypt's national security.

The newspaper, quoting the intelligence report, charged that LaHood, who heads the IRI office in Egypt, had advised his employees not to disclose their foreign nationalities under any circumstances. The charges against Lahood partly stem from the testimony of a woman named Dawlat Sweillam, who allegedly quit her job at IRI because of what she believed were activities that ran counter to Egyptian laws, according to the newspaper report.

Activists blame Mubarak-era laws that have been used to go after groups critical of state policies.