Israel's assault on Gaza sends more sparks flying into a combustible Middle East but is unlikely to ignite a wider war or destroy the Jewish state's 1979 peace treaty with Egypt.
A Hamas rocket killed three Israelis north of the Gaza Strip on Thursday and Israeli bombs brought the Palestinian toll to 13 in a worsening military showdown after Israel assassinated a top Hamas military commander the previous day.
Hamas, an offshoot of Egypt's Muslim Brotherhood, has become assertive in recent weeks, buoyed by a visit to Gaza by the emir of Qatar and by an apparent belief that Israel would not risk strong military action with Islamists ruling Egypt.
Egypt's Islamist president Mohamed Mursi, who has demanded that Washington rein in Israel's "unacceptable" attacks, faces popular pressure to act tough, but jettisoning the peace treaty would incur grave risks for a country still in turmoil after last year's revolt against Hosni Mubarak, who upheld it for 30 years.
However, US president Barack Obama, in telephone calls with Mursi and Israel's prime minister Benjamin Netanyahu on Wednesday, merely emphasised Israel's right to self-defence and gave no hint that he was considering any new push for peace with the Palestinians.
Cairo receives $1.3 billion a year in US military aid and looks to Washington for help with its ailing economy, constraining Mursi despite his need to show Egyptians that his policies differ from those of his US-backed predecessor.
"Mursi cannot do anything beyond reaching out to the international community because the balance of power in the region is tilted towards Israel," said Nabil Abdel Fattah, at Cairo's Ahram Centre for Political and Strategic Studies. "Arab countries also remain too weak militarily and diplomatically for any serious push against such aggression."
Obama has other headaches in West Asia for his second term, from the nuclear dispute with Iran to instability in Iraq and a conflict in Syria that has caused sometimes violent tensions on borders with Turkey, Lebanon, Iraq, Jordan and Israel.
The sectarian element in the Syrian struggle between mostly Sunni Muslim rebels and president Bashar al-Assad's Alawite-dominated rule fuels wider Sunni-Shi'ite rivalry in which Sunni-led states confront Shi'ite Iran, Assad's closest ally. This has estranged Hamas from some of its old friends.
The Sunni Islamist movement was once aligned with Shi'ite Hezbollah, Iran and Syria in an "axis of resistance" to Israel and the United States, but Assad's bloody crackdown on his opponents prompted it to break with Damascus earlier this year.
The pent-up frustration that burst into Arab uprisings last year has toppled four entrenched rulers so far. Popular unrest has flared in Jordan, Kuwait and Bahrain in the past week. Arab rulers, whether autocratic survivors or newly installed by the ballot box, must pay more heed to the sentiments of their citizens, overwhelmingly sympathetic to the Palestinians.
Yet, while it has again inflamed Arab anger, Israel's latest effort to deter rocket fire from Hamas militants in the densely populated Gaza Strip may well pass without an armed response from other Israeli foes such as Iran, Syria and Hezbollah.
Timur Goksel, a former UN peacekeeping adviser in Lebanon, said he expected no regional outgrowth to a familiar conflict beyond strongly worded condemnations from Arab leaders. "The only way this would get bigger is if Israel chose to take it to the next step [in Gaza]. That is Israel's decision and it isn't easy to guess because the Israelis have elections coming," he said. "If they leave it as is, it will die down."
Israel's military might is a daunting deterrent to any challenger, even one as battle-hardened as Lebanon's Hezbollah. The powerful Shi'ite movement fought Israel to a standstill in Lebanon in 2006 but stayed its hand during the last Israeli onslaught on Gaza in 2008-09 and will be wary of provoking another devastating war by firing rockets across the border.
Non-Arab Iran, savaged by Western sanctions, already faces Israeli threats to attack its nuclear facilities and, although it denies aspiring to match Israel's presumed nuclear arsenal, seems unlikely to plunge into an all-out conflict over Gaza.
Syria is preoccupied by its internal agony and is in no position to take on Israel. Still, exchanges of fire this week have broken decades of quiet on the line between Syria and the Israeli-occupied Golan Heights, fuelling speculation that Assad might stir trouble there as a diversion from his own plight.
The Gaza confrontation might briefly distract attention from Syria but would not greatly affect the conflict there, according to Beirut-based commentator Rami Khouri, who said the Israel-Hamas struggle had its own recurrent dynamic.
"The new outburst of violence is not surprising because there has been a consistent strategy of resistance by several groups to fire at Israel in response to the blockade," he said, referring to Israeli restrictions on the Gaza enclave. "It's not surprising because the situation there isn't sustainable," Khouri said.
For many Israelis, it is not sustainable either. During this year's cycle of violence and revenge, nearly 800 rockets from Gaza landed in southern Israel, disrupting life there and putting political pressure on Netanyahu, who faces a parliamentary election in January, to respond.
Israel is indeed concerned about possible Egyptian reaction — the government this month disavowed comments by senior defence ministry aide Amos Gilad that Egypt's Brotherhood was running a "shocking" dictatorship — but this has not tied its hands.
"Today we relayed a clear message to the Hamas organisation and other terrorist organisations," Netanyahu said on Wednesday, adding that Israel would broaden the assault if the need arose.
Israel has not ruled out a ground invasion as part of the military operation which started on Wednesday. Hamas's armed wing has called for revenge, saying: "The occupation has opened the gates of hell."
Additional reporting by Erika Solomon in Beirut, Marwa Awad in Cairo and Crispian Balmer in Jerusalem