An Egyptian court adjourned the trial of dozens of democracy activists including 16 Americans on Sunday at the opening session of a case that has threatened ties between Cairo and Washington and $1.3 billion in annual US military aid.

Forty-three foreign and Egyptian non-profit workers - including the son of the US transportation secretary - are accused of receiving illegal funds from abroad and carrying out political activities unrelated to their civil society work.

Judge Mahmud Mohamed Shukry adjourned the trial until April 26 at the end of the session in the rowdy chamber, where television reporters crowded around him and an interior ministry official threatened to expel journalists.

His decision could give more time for a diplomatic solution to the case, lawyers said.

'The time set allows for the NGO law to be amended and this could leave room for lawyers to argue that the defendants are not guilty. A fine may be demanded however,' said Khaled Suleiman, a lawyer acting against the defendants.

In the crowded courtroom on the outskirts of Cairo, lawyers who said they were volunteering in the case against the activists, demanded the defendants be imprisoned and accused them of 'espionage'.

'These organisations are accused of espionage and going against the law. Most of them are in contact with the CIA. These organisations gathered information and reports on Egypt and sent them to the US State Department,' the lawyer Suleiman said.

Judge Shukry said the defendants were free to leave the court and would not be held in detention until the next hearing.

Those accused in the case were banned from leaving Egypt pending the trial and some of the US citizens targeted in the probe have taken refuge at the American embassy.

Thirteen defendants stood behind the courtroom's bars on Sunday, all Egyptians. They appeared to be relaxed during recesses, using their mobile phones and talking to one another.

Several of the accused foreigners were already abroad when the travel ban was enacted. Many of the activists had not been formally summoned to appear before the court.

A senior US official said on Saturday Washington and Cairo were holding what he described as 'intense discussions' to resolve the crisis within days.

Secretary of State Hillary Clinton, who arrived in the Moroccan capital after visits to Algeria and Tunisia, has met Egypt's Foreign Minister Mohamed Kamel Amr twice in the last three days, the official said on condition of anonymity.

The US pro-democracy groups whose staff have been charged deny they have done anything illegal.

Egypt says the case is a judicial matter and all groups must heed Egyptian law. In the text of the charges the prosecution would present, the groups are accused of establishing without permission branches for their organisations and offering unauthorised political training and workshops to parties.

One of the judges leading the probe has said the non-governmental organisations had violated Egyptian tax laws by not declaring their income from abroad or paying taxes on their workers' pay and had carried out political activities unrelated to their civil society work.

Negad al-Borai, a lawyer representing the accused in Cairo, said the charges referred only to a short period in the groups' activities and could therefore be argued against.

'The charges made involve only the period from March 2011 to December 2011,' he told Reuters. 'These groups have applied for permits before that period.'  - Reuters