CAIRO, Egypt (AP) — Dozens of activists, mostly from Egypt's opposition Muslim Brotherhood, were arrested Monday after attempting to send a supply convoy to the blockaded Gaza Strip, the organization and security officials said.

Abdel-Fatah Rizq, who was coordinating the convoy for Egypt's biggest opposition group, said police arrested at least 50 activists as they gathered at the Journalists' Syndicate in downtown Cairo for the 200 mile journey across the Sinai desert to the border crossing of Rafah.

Rizq said other activists were planning to join the convoy on its way through the Sinai. The Brotherhood Web site said some activists, including parliament members, had managed to slip through security and reached the border.

Police said three members of the Brotherhood were arrested at the Suez Canal on Sunday night while trying to reach the border. In Rafah, another 14 activists from the secular Kifaya movement were arrested while staging a protest. Public demonstrations are not tolerated in Egypt.

In Cairo, thousands of riot police and plainclothes officers surrounded the streets around the syndicate Monday and chased activists into nearby buildings. Several journalists were detained and their cameras were confiscated.

Organizers then decided to halt the convoy attempt in hopes of negotiating the release of the detainees, said Mahmoud el-Khodairy, a retired judge and Brotherhood member.

"It is a shame that police have turned downtown Cairo into a garrison to harass a few dozen young people," el-Khodairy said. Police have said similar gatherings in the past caused public disorder.

Sympathy for the Palestinians blockaded in Gaza by Egypt and Israel runs high among Egyptians. The opposition periodically attempts to send food and medicine convoys to the border, partly to embarrass the government for its role in the blockade.

Meanwhile, Egyptian President Hosni Mubarak said Egypt would not permanently reopen the crossing as long as Hamas controls Gaza.

"We are still committed to the 2005 agreement," Mubarak was quoted as saying by state media Monday, referring to the agreement under which the Palestinian authority, Israel and EU monitors supervise the Rafah crossing.

Hamas wrested control of Gaza in June 2007, prompting the blockade by Israel and Egypt.