* Hamas throws down gauntlet to Abbas in West Bank
* Attack's consequences will deepen Palestinian divide
* Hamas promises attacks, PA promises arrests
By Tom Perry
RAMALLAH, West Bank, Sept 1 (Reuters) - A lethal attack by Hamas militants on Jewish settlers in the West Bank is as much a challenge to the Western-backed Palestinian Authority as it is to Israel, and seems bound to deepen the Palestinian divide.
The armed wing of the Islamist group threw down the gauntlet to President Mahmoud Abbas on Tuesday by killing four Israelis in the occupied territory where his security forces, retrained with U.S. support, have worked to prevent such violence. The attack was proof Hamas has survived what it describes as Abbas's efforts to "uproot" it from the West Bank.
It immediately exacerbated tensions between him and the militant rival movement, whose stronghold is the Gaza Strip, vacated by Israeli forces five years ago.
On the eve of peace talks in Washington, Abbas's security forces rounded up Hamas activists in the West Bank. The Iranian-backed Islamists called this an act of treason.
"The operation will deepen the divide," said Palestinian commentator Hany al-Masri, who has played a role in efforts to reconcile the two groups despite their fundamental differences over the future with Israel and their rival foreign allies.
The Hamas armed wing, the Izz el-Deen al-Qassam Brigades, promises more attacks. A senior security official in Abbas's administration promises more arrests.
Some 250 people associated with Hamas in the West Bank were rounded up on Wednesday, the group said.
SECURITY SHATTERED
The shooting was the deadliest attack on Israelis in the West Bank in four years. It jolted a security situation which Jewish settlers had said was never better. The Palestinian Authority says stability is in the Palestinian interest.
"The aim of the operation is to send a message to Israel, Abu Mazen and others that Hamas does exist and it can disrupt your plans," a senior Hamas official in the West Bank told Reuters, using Abbas's popular name.
"The other message is to say that Abu Mazen cannot protect the security of the Israelis and the settlers, despite arrests."
The chasm between the Palestinian rivals was reflected in their rhetoric. Naming its operation "The Flood of Fire", the Qassam Brigades said the attack was a "continuation of the jihad and resistance project against the Zionist enemy until the liberation of the land".
Abbas was due to launch direct peace talks in Thursday with Israeli Prime Minister Benjamin Netnyahu, seeking a treaty that would end the six-decade old conflict by creating a Palestinian state in the West Bank and Gaza at peace with Israel.
Hamas, part of an alliance including Iran, Syria and Lebanon's Hezbollah, has long opposed the negotiation process.
The group says it backs creation of a Palestinian state on lands occupied by Israel in 1967, but will only sign up to a long-term truce, not a permanent peace. Its charter calls for Israel's destruction.
Salam Fayyad, Abbas's prime minister, said bloodshed was "incompatible with Palestinian interests" and warned the Palestinians against being "sucked into a spiral of violence".
"Renouncing violence is the path to salvation, not exploiting the suffering of the Palestinian people in the service of factional and regional agendas," said Fayyad, who promotes non-violent activism against Israeli occupation.
(Additional reporting by Mohammed Assadi; Editing by Douglas Hamilton and Samia Nakhoul)
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