CAIRO (Reuters) - Egyptian security services barred members of four human rights groups from attending the closed military trial on Sunday of officials from the Muslim Brotherhood opposition group, a human rights activist said.

Elijah Zarwan, a consultant for the U.S.-based Human Rights Watch said he had been stopped from attending the trial along with members of Amnesty International, the Egyptian Organisation for Human Rights and the Arab Commission for Human Rights.

"We spent four hours negotiating with the security ... but we were turned away in the end," he told Reuters.

"The fact we were kept out reinforces our concerns that civilians cannot get a fair trial from a military court."

Military trials in Egypt are usually held behind closed doors. Attendance requires a special permit from the court.

Forty members of the Muslim Brotherhood, Egypt's strongest opposition group, are being tried on charges including money laundering and terrorism. They include the group's third-in-command Khairat el-Shatir, in custody since December.

The trial was adjourned until July 15, a court source said.

The Brotherhood operates openly despite having been banned since 1954. Members standing as independents won nearly one-fifth of the seats in parliament's lower house in general elections in 2005.

Analysts have said the trial represents the escalation of a government crackdown on the non-violent Islamist group to prevent it making further electoral gains that might present a serious threat to the rule of President Hosni Mubarak.