Palestinian President Mahmoud Abbas's Fatah group said Hamas forces arrested dozens of its activists in the GazaStrip on Thursday in an attempt to sabotage Egyptian efforts to reconcile the rival factions.
Nine of the detainees, including a senior Fatah lawmaker, were later released but about 40 others remained in custody, Fatah sources said.
Egypt hopes to end the factional fighting by hosting unity talks from November 9.
Tensions have remained high between the groups since Hamas Islamists seized the Gaza Strip in June 2007 after routing Fatah forces loyal to Palestinian President Mahmoud Abbas.
A Fatah spokesman said the latest arrests were an attempt by Hamas to sabotage the Cairo talks before they begin.
A Hamas government spokesman was not immediately available for comment.
Hamas has threatened to boycott the unity talks unless Fatah security forces released 400 Hamas activists being detained in the West Bank, where Abbas's government is based.
It is unclear whether the Cairo meeting will succeed in bridging the gaps between the factions. Previous Arab efforts met with failure, leading to more violence.
The split has divided the Palestinian territories, with Abbas's Western-backed government in the Israeli-occupied West Bank and a rival Hamas administration controlling Gaza.
Israel has ruled out implementing any statehood deal with Abbas as long as Hamas, who refuses to renounce violence and recognize Israel, controls the coastal territory.
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