Operation Pillar of Defence has been anticipated for many months following increasing rocket fire into Israel from Gaza, which one former Israeli military commander described yesterday as “holding hostage half the population”.

But the risks of a major military operation in the changing landscape of the Middle East are enormous.

In Gaza itself, the emergence of radical militant organisations, largely beyond the control of the ruling Hamas, make the consequences of Israel's operation highly unpredictable.

Hamas itself has felt the heat from these ultra-extremist groups, whose members claim the ruling faction has abandoned military resistance against Israel for the comfort and privileges of quasi-government.

These jihadist groups have close ties with militants in the Egyptian Sinai, just across Gaza's southern border, which Israel says are driven by an ideology akin to that of Al Qaeda. They are disinclined to listen to Egyptian government mediators, who have brokered a series of ceasefires following escalations of violence.

“There are more jihadist groups in Gaza who don't abide by the rules of the game,” said retired Brigadier-General Michael Herzog, a former chief of staff in the Israeli ministry of defence. “The Egyptians don't have the same leverage with the jihadists as they do with Hamas.”

Some analysts in Israel have warned that if Hamas were to be toppled in a sustained military operation, such groups could fill a power vacuum. Israel could conceivably find itself with an enemy even worse than Hamas, they say.

Egypt is another major cause of concern. Before its revolution in the spring of 2011, Israel could count on the support of the country's deposed president Hosni Mubarak. But his successor, Mohammed Morsi, who has long ties with the Muslim Brotherhood — Hamas's parent organisation — is likely to vehemently oppose the latest Israeli operation. It could even threaten the 1979 peace treaty between Israel and Egypt.

The offensive against Gaza may also ignite solidarity action from Hezbollah in Lebanon. Israel's border with Lebanon has been relatively quiet since the war in 2006, but Israel repeatedly says that Hezbollah has thousands of Iranian-supplied rockets aimed at the Jewish state.

There will also be international condemnation if the Israeli military operation causes widespread civilian casualties in Gaza. In Operation Cast Lead, the 22-day offensive which began in December 2008, around 1,400 people were killed in Gaza, including more than 300 children. Thousands of homes and schools were destroyed in intense bombardment. Israeli airstrikes are now much more precisely targeted. But civilian casualties are inevitable in a major operation.

Cast Lead took place between Barack Obama's election and his inauguration, which limited US response. Since then, Obama has repeatedly said Israel has the right to defend itself against rocket attacks from Gaza, but his re-election may produce much sharper condemnation of civilian casualties than four years ago.

Israel is also going to the polls in January. Most Israeli politicians swiftly endorsed yesterday's operation mindful that security is a major factor in all Israeli elections.

By arrangement with the Guardian

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