Egyptian soldiers and police stormed non-governmental organisation offices throughout the country today, banning employees inside from leaving while they interrogated them and searched through computer files, an activist and security official said.
Egyptian state television reported at least 18 offices were targeted in the raid.
In Cairo, an Egyptian court acquitted five policemen of charges of killing five protesters and wounding six others during the 18-day uprising that toppled Hosni Mubarak's regime on 11 February. Over 800 protesters were killed in the protests that began on 25 January.
The court said three of the defendants were not at the site of the killings while the two others fired against protesters in self defence.
The raids and the acquittal of the policemen were certain to usher in a new low in relations between the ruling generals who took over from Mubarak and rights groups and activists who engineered the uprising that ousted him.
Relations between the two sides have been fraught with tension for months, mainly over the military's handling of the transition, its human rights record and its failure to restore security or revive the economy.
The raids were likely to spur new charges from reformists that the military is continuing the harsh practices of the deposed regime.
US-based organisations, including the National Democratic Institute, the International Republican Institute and Freedom House, were among those being searched. Several local Egyptian rights groups that receive foreign funding were also raided.
The head of the Arabic Network for Human Rights Information, Gamal Eid, said an employee trapped inside one of the NGO's called him to say security forces are removing laptops.
Armed security forces were seen stationed outside several of the offices being raided, banning anyone from entering or speaking with employees inside.
An official with the Egyptian Attorney General's office said at least one of the US-based organisations was operating without proper permits.