Israel has detained 10 senior Hamas leaders in the West Bank two days after indirect talks between the two sides on a possible prisoner swap collapsed.
An Israeli military spokeswomen described them as "terror operatives"; Hamas said they included four MPs, a former deputy PM and an academic.
Israeli forces and the rival West Bank Palestinian leadership have clamped down on the militant group since 2007.
That was when Hamas took sole control of Gaza, which is blockaded by Israel.
The detainees include Nasser Shaer, who served as Palestinian Authority deputy prime minister when Hamas won PA legislative elections in 2006.
He was arrested in Nablus. Three others, including an MP and a mayor were arrested in Ramallah, and another MP was taken in the Jenin area.
Correspondents say the detentions appear to be an Israeli attempt to pressure Hamas after the failure of recent efforts to win the release of captured soldier Gilad Shalit, who is being held by Hamas in Gaza.
"These men have been the leaders of the ongoing effort to restore the administrative branch of the Hamas terror organisation in the region, while attempting to strengthen the power and influence of Hamas," the Israeli spokeswoman said.
Speaking from Gaza, Hamas official Ahmed Bahar denounced the arrests as "immoral blackmail by the Zionist occupation".
More than 30 Hamas MPs remain in prison in Israel after being arrested in the wake of Gilad Shalit's capture in 2006.
Hamas has been demanding the release of more than 400 of the thousands of Palestinian prisoners held by Israel.
An Israeli military official quoted by Reuters said there was "no indication" the arrests were connected to the Shalit issue.
Shalit negotiation
Outgoing Israeli Prime Minister Ehud Olmert had hoped to secure the release of Sgt Shalit before the formation of a new Israeli government, which could happen within days under the authority of PM-designate Benjamin Netanyahu.
The right-wing former premier is seen by analysts as less likely to reach a compromise than Mr Olmert. Mr Olmert sent two senior envoys to Cairo at the weekend hoping to seal a deal to swap Sgt Shalit for hundreds of Palestinian detainees, but they returned empty handed.
Each sides blamed the other for the collapse, the Israelis saying Hamas had hardened its position and Hamas saying Israel had brought nothing new to the talks.
The Shalit family set up a protest tent in front of Mr Olmert's house last week, escalating their campaign towards the end of his term in office.
They now say they intend to dismantle the camp on Sunday, which will be their son's 1,000th day in captivity.
Nothing has been heard from the Israeli conscript since June 2008, two years after his capture, when a letter in his handwriting was delivered to the Carter Centre in Ramallah in the West Bank.
Gilad Shalit, then a corporal, was captured by Palestinian militants from Gaza, including some from Hamas's armed wing, in a cross-border raid in June 2006.
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