A terrible sense of foreboding set in when, for the first time in decades, rockets were launched on Jerusalem, a city holy to Jews and Muslims alike, on Friday. It was as if, in a country where conflict is a commonplace, a red line had been wilfully crossed. Targeting Jerusalem was more dramatic even than rockets reaching Tel Aviv the day before, setting off the first air-raid warning in Israel's great commercial and cultural metropolis since Iraqi Scud missiles were fired at the city by Saddam Hussein in 1991. Israel has reacted with brutal ferocity. There seems worse to come.

It is wrong to suggest, as many have, that this is strong-man posturing got out of hand by Israel's bellicose leader Benjamin Netanyahu ahead of a general election in two months' time. There are parallels between now and Israel's attacks on Lebanon in 1996 and Gaza in 2008 – both on the eve of elections – but there are also differences which make things today much more dangerous.

After last week's assassination by Israel of Ahmed al-Jabari, the military leader of the Palestinian faction which has controlled Gaza since 2007, a Hamas spokesman declared "there are no more red lines", with a vow to resume the suicide bombings that terrorised Israeli cities a decade ago. Resistance possibilities, he said, were now unlimited. The world should take that statement seriously.

Something was already going on in Hamas which is said to have stockpiled 11,000 Iranian-built missiles over the past four years and yet till now used only a few of them. In 2010, only 231 rockets from Gaza hit Israeli towns, according to the Israeli Defence Force. In 2011 the figure was 627. This year that has doubled to more than 1,200 – a third of them in the few days since the assassination of Jabari, striking targets as far away as Dimona, the home of Israel's nuclear reactor. Israel has responded ferociously, with about 800 air and artillery strikes on Gaza.

So why has Hamas upped the attacks? Some suggest that a ceasefire between Israel and Hamas was being negotiated, through Egyptian intelligence; hours before he was assassinated, Jabari had received a draft permanent truce agreement. But then the Israelis decided that the Hamas leader, who had kept resistance to a token level for years, was no longer able to control the more violent Palestinian factions such as Islamic Jihad in Gaza. So he was killed.

Whether or not such close-focused Machiavellian detail is true, what is indisputable is that massive geo-strategic influences are at work. The pieces of the complicated puzzle that is the Middle East have shifted significantly with the Arab Spring.

In the old days, the Arab world was divided between allies of the West – Egypt, Jordan, the Gulf states, Saudi Arabia and much of the Maghreb – and those resistant to US interests and influence – Iran, Syria, Iraq and Hezbollah. But the kaleidoscope has been shaken. The loudest voices of support for the Palestinians now come from such US allies as Egypt and Qatar. "Moderate Arabs" are too preoccupied with their own troubles as the Arab revolutions threaten to bring Islamists greater influence in Jordan, Kuwait, Bahrain, the Emirates and Saudi Arabia.

Egypt, once America's best Arab ally and Israel's least hostile neighbour, now has a president from the Muslim Brotherhood which spent decades attacking Egypt's previous leader for his peace deal with the Jewish state. The Palestinian cause is more popular than ever in the Arab world. Last month, the Emir of Qatar visited Gaza. So did Egypt's Prime Minister on Thursday to hold the bloodied body of a young Palestinian boy killed during the fighting. The Tunisian foreign minister was due there yesterday. Hamas is newly emboldened.

What adds to the volatility is the turmoil across the region. Syria is in civil war. Lebanon is unstable. Turkey is unnerved. There are protests in Jordan, the Gulf states and parts of Saudi Arabia as the febrile contagion of the Arab Spring spreads. Then there is Iran, whose nuclear programme Benjamin Netanyahu has repeatedly described as the biggest threat to Israel's security. Israel's army chief of staff and the director of Mossad refused to attack Iran's nuclear facilities in 2010 when Netanyahu asked them to. There are insistent rumours that there have been secret back-channel contacts between Ayatollah Khamenei's foreign affairs adviser, Ali Akbar Velayati, and Washington. That, and an Obama second term untrammelled by the need for re-election, have unnerved Netanyahu. But if he cannot attack Iran he can bomb Gaza instead.

There is another key factor. There are power struggles within the Palestinians, between Hamas's leaders in Gaza and those in exile in Cairo, and between Hamas and the Fatah movement that controls the West Bank. Fatah, now convinced that years of endless US-led peace talks were merely a cover for Israel to continue building illegal settlements on Palestinian land, will at the end of this month apply for observer status at the United Nations for Palestine as an independent sovereign state. That would allow the Palestinians to join the International Criminal Court and bring a deluge of criminal cases against Israeli officials and soldiers. The Jewish state would then be under siege from more than missiles – and the balance of Palestinian power could switch from Hamas to Fatah.