Egyptian police have rounded up hundreds of members of the Muslim Brotherhood group accused of holding illegal protests against Israel.
Routed demonstrators regrouped at the lawyers' syndicate
Riot and plainclothes police broke up a pro-Palestinian demonstration near the Arab League headquarters in central Cairo with batons and tear gas.
The protest was called to press the Egyptian government to do more to help people in the blockaded Gaza Strip.
The arrests come amid a crackdown on the Brotherhood ahead of council polls.
Security forces chased Brotherhood members through the streets of central Cairo as they gathered in Tahrir Square, but demonstrators were able to regroup away from the planned protest venue.
Protesters shouted: "Gaza residents, we are with you night and day" and "Keep strong Haniya, don't let go of your gun" in reference to the ousted Palestinian Prime Minister Ismail Haniya of the militant Hamas movement that controls Gaza.
Security officials, quoted by Associated Press news agency, said 460 members, including leading figures, had been rounded up to prevent the demonstration.
Security sources say police had earlier in the week arrested more than 50 Brotherhood members in raids in Cairo, Alexandria and parts of the Nile Delta.
The non-violent Brotherhood is Egypt's most popular opposition group; it is banned by law, but activists participate in elections as independent candidates.
Egypt has been kept under emergency rule since 1981, giving the authorities sweeping powers to quash demonstrations and arrest suspects.
Brotherhood leaders have been accusing the Egyptian government of collaborating in Israel's blockade of Gaza to put pressure on Hamas, with which the Brotherhood shares close ties.
However, on Wednesday many of the border defences were breached from the Gaza side and Egyptian security forces stood by as Gazans streamed across to buy food and other supplies.
Israel says its blockade is to stop Palestinian militants firing rockets into southern Israel, but it has been condemned as collective punishment by the European Union and international agencies.
Egypt is preparing to hold municipal elections by March after a postponement of two years.
In the 2005 parliamentary elections, the Brotherhood sent shockwaves through the ruling National Democratic Party by attracting strong support, winning one-fifth of seats despite what observers said was an unfair vote.