By Samia Nakhoul, Nidal al-Mughrabi, Matt Spetalnick and Laila Bassam

DUBAI/GAZA/WASHINGTON When Islamist group Hamas launched a spectacular attack against Israel, it also took aim at efforts to forge new regional security alignments that could threaten Palestinian aspirations for statehood and the ambitions of the group's main backer Iran.

Saturday's assault, the biggest incursion into Israel in decades, coincides with U.S.-backed moves to push Saudi Arabia towards normalising ties with Israel in return for a defence deal between Washington and Riyadh, a move that would slam the brakes on the kingdom's recent rapprochement with Tehran.

Palestinian officials and a regional source said the gunmen who stormed Israeli towns, killing 250 Israelis and taking hostages, were also delivering a message that the Palestinians could not be ignored if Israel wanted security and that any Saudi deal would scupper the detente with Iran.

More than 250 Gazans have been killed in Israel's response.

"All the agreements of normalisation that you (Arab states) signed with (Israel) will not end this conflict," Ismail Haniyeh, the leader of Hamas which runs Gaza, said on Al Jazeera television.

A regional source familiar with the thinking of Iran and that of the Iranian-backed Lebanese group Hezbollah added: "This is a message to Saudi Arabia, which is crawling towards Israel, and to the Americans who are supporting normalisation and supporting Israel. There is no security in the whole region as long as Palestinians are left outside of the equation."

"What happened is beyond any expectation," the source said. "Today is a turning point in the conflict."

The Hamas attack launched from Gaza follows months of rising violence in the Israeli-occupied West Bank, with stepped-up Israeli raids, Palestinian street attacks and assaults by Jewish settlers on Palestinian villages. Conditions for Palestinians have worsened under the hard-right government of Prime Minister Benjamin Netanyahu. Peacemaking has been stalled for years.

Meanwhile, Saudi Arabia and Israel have both indicated they are moving closer to a normalisation deal. But sources previously told Reuters the kingdom's determination to secure a U.S. defence pact meant it would not hold up a normalisation agreement to win substantive concessions for the Palestinians.

Laura Blumenfeld, a Middle East analyst at the Johns Hopkins School for Advanced International Studies in Washington, said Hamas may have lashed out due to a sense that it was facing irrelevance as efforts advanced toward broader Israeli-Arab relations.

"As Hamas watched the Israelis and Saudis move close to an agreement, they decided: no seat at the table? Poison the meal,” she said.

TIMING THE ASSAULT

Osama Hamdan, the leader of Hamas in Lebanon, told Reuters that Saturday's operation should make Arab states realise that accepting Israeli security demands would not bring peace.

"For those who want stability and peace in the region, the starting point must be to end the Israeli occupation," he said. "Some (Arab states) unfortunately started imagining that Israel could be the gateway for America to defend their security."

Netanyahu promised "mighty vengeance for this black day" after the launch of Saturday's attack, which came almost exactly 50 years since the start of the Yom Kippur War in 1973 when Israel was attacked by Egyptian and Syrian forces and fought for its survival.

Mirroring the timing of the 1973 war, Hamas official Ali Baraka said of Saturday's assault: "It was necessary that the leadership of the resistance take a decision at the appropriate time, when the enemy is distracted with its feasts."

He said the assault by air, land and sea was "a shock to the enemy and proved the Israeli military intelligence failed to find out about this operation," after Israel, which prides itself on its infiltration and monitoring of militants, was taken by surprise.

In the years since 1973, Egypt signed a peace treaty with Israel and several other Arab states have also since normalised ties, including some Gulf Arab states next to Saudi Arabia. But the Palestinians have moved no closer to their aspiration of securing a state, which looks as distant a prospect as ever.

"While not likely the main driver of the attacks, Hamas’s actions send a clear reminder to the Saudis that the Palestinian issue should not be treated as just another subtopic in normalisation negotiations," Richard LeBaron, a former U.S. Middle East diplomat now at the Atlantic Council thinktank, wrote.

IRAN'S REACH

A senior official in U.S. President Joe Biden's administration told reporters it was "really premature to speculate" about the effect the Israeli-Hamas conflict could have on efforts towards Saudi-Israeli normalisation.

"I would say for certain Hamas, terrorist groups like Hamas, will not derail any such outcome. But that process has a ways to go," added the official, speaking on conditional of anonymity.

Netanyahu has previously said the Palestinians should not be allowed to veto any new Israeli peace deals with Arab states.

A regional source familiar with the Saudi-Israeli-U.S. negotiations over normalisation and a defence pact for the kingdom said Israel was committing a mistake by refusing to make concessions to the Palestinians.

In its response to Saturday's attacks, Saudi Arabia called for an "immediate cessation of violence" between both sides.

Iran, meanwhile, has made no secret of its backing for Hamas, funding and arming the group and another Palestinian militant organisation Islamic Jihad. Tehran called Saturday's attack an act of self-defence by Palestinians.

Yahya Rahim Safavi, adviser to Iran's Supreme Leader Ayatollah Ali Khamenei, said Tehran would stand by the Palestinian fighters "until the liberation of Palestine and Jerusalem."

A Palestinian official, close to Islamist militant groups, said after the Hamas attack began with a huge barrage of rockets fired from Gaza: "Iran has hands, not one hand, in every rocket that is fired into Israel."

"It doesn't mean that they ordered (Saturday's) attack but it is not a secret that it is thanks to Iran, (that) Hamas and the Islamic Jihad have been able to upgrade their arsenal," said the official, speaking on condition of anonymity.

Iran's backing for Palestinian groups is part of a broader network of militias and armed groups it supports across the Middle East, giving Tehran a powerful presence in Lebanon, Syria, Iraq and Yemen, as well as Gaza.

Analysts said Iran already appeared to have sent a signal last week that a Saudi deal would hit Riyadh's detente with Tehran, when Yemen's Iran-backed Houthi group killed four Bahraini soldiers in a cross-border strike near the Saudi-Yemeni border. That attack jeopardised peace talks to end Yemen's eight-year conflict.

Dennis Ross, a former Middle East negotiator who is now at the Washington Institute for Near East Policy in Washington, added: "This is all about preventing the U.S.-Saudi-Israel breakthrough."

(Reporting by Samia Nakhoul and Parisa Hafezi in Dubai, Nidal El Mughrabi in Gaza, Laila Bassam in Beirut, Matt Spetalnick in Washington; Writing by Samia Nakhoul; Editing by Edmund Blair)