CAIRO – The trial of 16 Americans and 27 others opens Sunday at a Cairo courthouse in what critics say is a politically charged case linked to a government crackdown on nonprofit groups that has touched off the deepest crisis in U.S.-Egyptian relations in decades.

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 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.

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.

The U.S. 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.

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 of 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 ruler 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.

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.

It is not clear whether the Americans and the rest of the defendants will appear in court Sunday. They could not be immediately reached by telephone.

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 Saturday 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.

While the trial involves foreign-funded NGOs, hundreds of Egyptian non-governmental organizations have also come under investigation from the government since Mubarak´s ouster.

Activists blame Mubarak-era laws that have been used to go after groups critical of state policies. ___ Associated Press writer Matthew Lee in Rabat, Morocco, contributed to this report. (© 2012 The Associated Press 02/25/12)