Hamas police in the Islamist-ruled Gaza Strip have rounded up dozens of members of Palestinian president Mahmud Abbas's secular Fatah movement, Fatah said on Saturday.
Spokesman Hassan Ahmad told AFP the arrests on Friday took place at a ceremony in Khan Yunis in the south of the coastal enclave.
"Hamas police intervened during a ceremony to honour martyrs" killed by Israel, Ahmad said.
"They arrested dozens of people for no reason."
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Islam Shahwan, a spokesman for the Hamas interior ministry, said police acted because the meeting organisers had not sought permission.
"Around 20 people were detained and later released after signing a document not to take part in unauthorised meetings," Shahwan said.
Fatah and Hamas, which rule in the West Bank and Gaza respectfully, signed a reconciliation agreement in Cairo in 2011 aimed at ending their political differences.
However, most clauses in the accord remain unimplemented.