An Egyptian court has opened the trial of 16 Americans and 27 other employees of foreign non-profit groups, in a case that has threatened ties between Cairo and Washington and $1.3 billion in annual U.S. military assistance.

Judge Mahmoud Mohammed Shoukry presided over a chaotic opening session Sunday, before adjourning the trial until April 26.

Television reporters crowded around him and an interior ministry official threatened to expel journalists from the rowdy Cairo chamber.

The thirteen Egyptian defendants who appeared in court were all released until the next hearing. Those accused in the case are barred from leaving Egypt, and some of the U.S. citizens targeted in the probe have taken refuge at the American Embassy in Cairo. Others left Egypt before the travel ban was enacted.

The 43 defendants – including the son of U.S. Transportation Secretary Ray LaHood – are accused of receiving illegal funds from abroad, carrying out political activities unrelated to their civil society work and failing to obtain the necessary operating licenses.

The groups say they have long sought to register in Egypt.

Speaking in Morocco Sunday, U.S. Secretary of State Hillary Clinton said American officials are evaluating the latest developments. The Obama administration is said to be in “intense discussions” with Egypt to resolve the issue.

Besides the 16 Americans and 16 Egyptian defendants in the case, the remaining suspects include Germans, Palestinians, Serbs and Jordanians.

The case comes as the United States is trying to establish better ties with the military council that took power last year following the ouster of former president Hosni Mubarak. Washington has warned that going forward with the trial could prompt a cut to Cairo's $1.3 billion in annual U.S. military aid.

U.S. legislators and Egyptian activists say the trial is politically motivated. Rights groups have sharply criticized the investigation, saying it is part of an orchestrated effort by authorities to silence groups critical of the military's handling of the country's democratic transition.

Egyptian officials counter by saying the trial has nothing to do with the government and is in the hands of the judiciary.

Also Sunday, Egypt's military rulers called on the newly elected parliament to convene on March 3 to elect a 100-member assembly tasked with writing the country's first constitution since Mr. Mubarak's overthrow.

A power struggle over the future document is rapidly developing between Egypt's army-backed executive and the Islamist-dominated parliament, which wants to curb broad presidential powers.

Political groups, led by the Muslim Brotherhood's Freedom and Justice Party, have already begun talks over the make-up of the constituent assembly. The panel is expected to include legal experts as well as legislators.