A five-month truce between Israel and the Islamist rulers of the Gaza Strip was foundering today after Israeli special forces entered the besieged territory and battled with Hamas militants, leaving six Palestinian fighters dead and four Israeli soldiers wounded.

The Israeli military described the operation as a “pinpoint” raid to destroy a 250-metre tunnel it said the hardline Palestinian movement was digging under the border to try to kidnap an Israeli soldier, as it did in summer 2006.

Hamas responded to the attack by firing more than 30 of its unguided Qassam rockets into southern Israel, causing no damage or injuries but reviving fears of the cross-border war of attrition that left scores of people dead, most of them Palestinians, before an Egyptian mediated truce came into force in June.

The fighting began when Israeli troops entered the central region of the Gaza Strip, which has been sealed off from the outside world since Hamas seized control 18 months ago. The unit attacked a house believed to be used as the starting point of the tunnel. Hamas fighters confronted the Israelis, using forces which they have built up and trained into a guerrilla army since taking full control of Gaza.

One Hamas militant was killed in the clashes, prompting a swift barrage of rocket fire at Israeli farming communities close to the Gaza boundary and in nearby Ashqelon, a medium-sized Israeli coastal city. Israeli forces responded by firing at the rocket launchers, with an air strike killing five more Hamas members as they tried to launch mortars into Israel.

“The Israelis began this tension and they must pay an expensive price,” said Fawzi Barhoum, a Hamas spokesman in Gaza. “They cannot leave us drowning in blood while they sleep soundly in their beds.”

Behind the angry rhetoric, however, neither side appeared interested in tearing up the fragile ceasefire which allowed both Israel and Hamas to escape from a difficult impasse. Israel has no interest in launching a massive and costly invasion of the territory it pulled out of three years ago, while Hamas’ rocket fire only served to tighten Israel’s stranglehold on the area it controls, destroying the economy and plunging the population into even deeper misery.

Mark Regev, an Israeli spokesman, said he hoped that calm would be restored and that a resumption of hostilities that had ground down the region for months could be avoided. “This operation was in response to a Hamas intrusion of the quiet and we hope we won’t see an escalation here,” he said.

Israeli military intelligence had been warning for weeks of plans by extremists to kidnap Israelis, either along the Gaza border or elsewhere in the world in response to the assassination of a Hezbollah militant leader earlier this year, which the Lebanese guerrilla organisation blamed on Israel.

Israel fought a bitter, month-long war with Hezbollah in 2006 following a cross-border raid to seize its troops on the northern border, an attack that followed the capture of an Israeli corporal, Gilad Shalit, in Gaza the month before. Corporal Shalit is still being held in a secret location in Gaza by Hamas, despite protracted talks mediated by Cairo to secure his release.

Hamas officials accused Israel of trying to disrupt talks next week in Cairo to try and heal the rift between itself and the mainstream Fatah movement that it kicked out of Gaza in heavy fighting in June 2007. Fatah still holds the West Bank and is conducting talks with Israel about a possible peace settlement, although negotiations have been seriously disrupted by the forced resignation of Ehud Olmert, the Israeli Prime Minister, over corruption allegations.

Into this tangled knot of three-way talks, each of them bogged down by mutual recriminations and intermittent violence, will walk Condoleezza Rice this week, on a last-ditch attempt to make good on US promises to secure at least the outline of a peace deal before the end of the year. President Bush largely neglected the complex conflict before last year launching a belated peace process which has failed to make much visible progress.

With Mr Olmert now on the way out, his successor Tzipi Livni, who has led recent peace talks with the Fatah leadership, faces a tight race with right-wing hawk Binyamin Netanyahu next February. Mr Netanyahu wants to give the Palestinians only limited sovereignty and refuses to discuss the division of Jerusalem, which the Palestinians see as a prerequisite for any peace deal.