Police in Egypt have blocked a convoy organised by opposition groups to carry medical supplies to the Gaza Strip.
The convoy had been due to leave from the journalists' syndicate in central Cairo but activists gathering there were surrounded by police.
Reports say at least 15 people were detained in Cairo - some of them linked to the Muslim Brotherhood.
Some activists were reportedly detained trying to cross into Sinai and some nearer Rafah.
The protest is being supported by other opposition groups in Egypt.
Egyptian police prevented a similar attempted protest by Islamists in September.
Under an agreement brokered by the US in 2005, the Palestinian Authority, Israel and European Union monitors supervise the Rafah crossing between Gaza and Egypt. Egypt has co-operated with this.
Hamas, which has governed Gaza since June 2007, has been kept out of this arrangement.
The Egyptian government has also co-operated in the Israeli blockade of Gaza, which Israel says aims to undermine support among Gaza Palestinians for the Islamist movement Hamas.
But many Egyptians oppose their government's policy.
The crossing at Rafah is closed almost all of the time.
But on Monday, reports from the Gaza Strip say, Egypt temporarily re-opened the crossing to allow a number of Palestinians to return home.
The reports say several dozen Palestinians were permitted through the crossing after returning from visiting Mecca in Saudi Arabia.
A spokesman for the Hamas authorities in Gaza said more pilgrims were expected to return to Gaza in the coming days.
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