The Israeli military has rounded up 379 militant activists, including dozens of electoral candidates from Hamas (search), prompting accusations that Israel is using a weekend truce breach as an excuse to crush the Islamic terrorist group before upcoming Palestinian elections.

The arrest sweep in the West Bank (search) — the biggest in three years and part of a new offensive against Hamas — came after Israel (search) failed to win international backing for its demand that the terrorist organization be barred from the Jan. 25 parliamentary vote.

Israel says a government that includes Hamas, which calls for the destruction of the Jewish state, would threaten peace prospects. But letting Hamas contest elections is the cornerstone of Palestinian leader Mahmoud Abbas' (search) plan to tame the group, and the Palestinian Authority believes it will be the main loser in the Israel-Hamas showdown.

The arrests, made over three days, are generating sympathy for Hamas and could further improve its strong electoral prospects. Abbas' ruling Fatah movement is widely perceived as corrupt, and many Palestinians say they will vote for Hamas to teach Fatah a lesson and get better government services. Many view Hamas as a much more disciplined organization that could bring order to the chaotic Gaza Strip.

On the other hand, if Israel arrests more candidates than Hamas can replace, it might decide to bow out of the election, a step that could lead to the cancellation of the vote and further undermine Abbas' claim to leadership.

"The Israeli interference is only complicating the situation for the Palestinian Authority," said Palestinian Planning Minister Ghassan Khatib.

Israel launched its offensive of airstrikes, targeted killings and mass arrests after Hamas fired scores of homemade rockets from Gaza at Israeli border towns over the weekend.

Early Wednesday, Israeli troops raided Hamas offices in the West Bank towns of Qalqiliya and Tulkarem, Palestinian security officials said. The army had no immediate comment on the raid.

Also Wednesday, in the fifth straight day of airstrikes, Israeli aircraft unleashed a barrage of missiles and fired artillery shells into the Gaza Strip for the first time. The strikes knocked out power to Gaza City and destroyed a bridge, but no injuries were reported.

The five-day offensive was the first major rocket barrage after Israel's pullout from Gaza in mid-September, but caused only minor injuries. Israel said it had to react strongly to make Hamas understand that new rules were in place after the pullout and that no attacks from Gaza would be tolerated.

The rocket fire also gave Israel an opportunity to renew a broader campaign against Hamas that had largely been put on hold after Abbas negotiated an informal truce in February, Israeli and Palestinian commentators said.

"This (the rocket fire) was a fatal error," military commentator Alex Fishman wrote in the Yediot Ahronot daily. "They played directly into the hands of Israel, which was just waiting for such an opportunity."

Even before the weekend violence, the head of Israel's domestic Shin Bet security service, Yuval Diskin, told reporters the rise of Hamas posed a serious threat to Israel. Diskin was quoted as saying he considered Hamas' attempt to grab power a "strategic problem" for Israel.

Hamas has carried out scores of fatal attacks against Israel and as a partner in an Abbas government could block future peace moves.

On Tuesday, Hamas militants released a video showing a bound and blindfolded man they claimed was an Israeli businessman they kidnapped last week and later killed in response to the Israeli offensive. Sasson Nuriel, a 51-year-old Jerusalem businessman, was found dead Monday.

The kidnapping and videotape appeared to signal a new tactic for Hamas. The group claimed it has formed a special unit to kidnap Israelis in a campaign to secure the release of thousands of Palestinian prisoners.

Hamas' rocket barrage was in response to a blast at a Hamas rally in Gaza that killed 21 people on Friday. Hamas said the explosion was caused by an Israeli missile, but both Israel and the Palestinian Authority said it was caused by militants mishandling explosives.

Israel arrested 82 Hamas and Islamic Jihad militants overnight Tuesday, in addition to 297 militants taken into custody in the previous two days, the military said. All the arrests took place in the West Bank, which Israel still occupies.

Hamas said that among the detainees were dozens of candidates for parliament and local councils, as well as campaign volunteers and sitting council members, including nine of 11 Hamas representatives in the village of Shuqbeh.

Many were taken from their homes, a sign they did not expect arrest. Those with ties to militants tend to stay in hiding or switch apartments and cars.

Hassan Yousef and Mohammed Ghazal, considered leading Hamas parliament candidates in the Ramallah and Nablus districts, also were arrested. Both are considered relative moderates because they have not ruled out negotiations with Israel.

Israel "is using every possible means to block Hamas and push it aside," said Hamas spokesman Mushir al-Masri. "Those arrested are leaders ... of the first and second level," he said, adding that Israel aims to "weaken Hamas, particularly before the legislative elections."

Israel said it does not differentiate between Hamas gunmen and politicians. "The entire leadership of Hamas is involved in the planning of murderous attacks against as many innocent civilians as possible," the military said in a statement.

Ranaan Gissin, spokesman to Israeli Prime Minister Ariel Sharon, said "they can't be political candidates and at the same time continue to act as terrorists."

Sharon adviser Zalman Shoval said Israel is trying to make Abbas understand that peace efforts could be frozen if he brings Hamas into his government.

However, Abbas has resisted disarming the group and instead offered it political participation in exchange for a truce.

The third of four rounds of local elections is to be held Thursday. Hamas has done well in previous local votes, wresting control of key towns from Fatah. The January parliamentary election will be the most crucial test of Hamas' political strength throughout the West Bank and Gaza Strip.

Hamas has not yet published its final list of parliament candidates and might keep it secret until just before the election to protect them from arrest, members of the group said.

It will be up to the Palestinian Authority to decide whether prisoners may run in the elections; in previous elections, it approved such an arrangement.

Sharon first raised the demand to disqualify Hamas when he met with foreign leaders during U.N. anniversary celebrations in New York two weeks ago. Sharon said that if the request is ignored, Israel could disrupt the voting, at least in the West Bank, by refusing to ease travel restrictions.

However, Secretary of State Condoleezza Rice has urged Israel not to interfere. "I think we have to give the Palestinians some room for the evolution of their political process," she said recently.