Israel's army early Wednesday arrested five members of the Palestinian Islamist group Hamas, including a member of parliament, a prisoners' support group said.
The five were arrested at dawn at their homes in the southern West Bank city of Hebron, the Ramallah-based Prisoners' Club told AFP.
They included Hamas MP Mohammed Jamal al-Natshe, it said.
An Israeli army spokeswoman said "six people were arrested and taken for security questioning," but gave no further details.
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The army later on Wednesday released another Hamas MP, Nayef al-Rujub, who had been in prison for two and a half years, the Prisoners' Club said in a statement.
The Israeli army had yet to confirm the release.
Israel has stepped up arrests of Hamas members in the West Bank, in the face of a rising tide of low-intensity conflict and civil unrest.
There are currently 13 Palestinian lawmakers in Israeli jails, including Natshe. Hamas has 74 members in the 132-seat Palestinian Legislative Council.