A fragile six-month ceasefire between Israel and the Palestinian militant faction Hamas in Gaza officially expires today, with the Islamist group Hamas refusing to enter talks to renew the six-month truce.

In reality, however, the calm had already expired more than a month ago, when an Israeli army raid to destroy a tunnel it said militants were digging under the border led to a renewed bout of Palestinian rocket fire.

More than 20 rockets were launched from Gaza into southern Israel yesterday, reviving fears of that the cross-border war of attrition - when Israeli raids in the crowded coastal territory met with daily barrages from Palestinian rocket teams - could once again terrorise residents on both sides of the heavily guarded boundary.

While Israel has insisted it wants to renew the truce, military planners have drawn up other scenarios: from raids against militant rocket-firing squads to a full-scale re-invasion of the Gaza Strip, from which Israel withdrew in 2005, evicting thousands of Jewish settlers.

"The calm ends on December 19 and Hamas’ position is against renewing the calm,” said Fawzi Barhoum, a spokesman for Hamas, which seized total control of the impoverished territory 18 months ago in bloody battles with its mainstream rival Fatah. Gaza’s economy has been destroyed since then, under siege from Israel which only allows the bare minimum of humanitarian assistance to enter in a bid to force an end to rocket attacks.

Latest UN figures showed that unemployment has risen to 49 per cent and that half of Gaza City’s residents receive water only once a week for a few hours. Homes are also without electricity for up to 16 hours a day.

“The factions’ duty after the calm expires is to protect the people, defend the Palestinian people and confront any aggression,” said Mr Barhoum. “The Zionist enemy bears the responsibility for the end of calm.”

Israel has little appetite for a full-scale invasion of Hamas, and is working on a local missile shield, called Iron Dome, which it says could be ready in a year. In the meantime, it is carrying out airstrikes and ground attacks against militants. In one large-scale operation before the current truce, Israeli forces killed more than 100 Palestinians in a single day.

The intractable situation in Gaza will be a major test for the new Israeli government to emerge from February’s hotly contested elections. Tzipi Livni, the serving Israeli Foreign Minister and head of the Kadima party, emerged in a strengthened position yesterday from her centre-right party’s internal elections.

With a more hawkish slate behind her, Ms Livni’s standing in opnion polls rallied slightly, with Kadima closing the gap on the hardline Likud party. Latest surveys showed Likud, led by the former Prime Minister Binyamin Netanyahu, winning 29 of the Knesset’s 120 seats, while Kadima, which leads the current coalition, could win 25. Labour, which is Kadima’s main coalition party and is led by Ehud Barak, the Defence Minister, would win just ten seats, a far cry from the decades when it dominated Israeli politics.

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