If Israel carries out threats of a massive offensive in the Hamas-ruled Gaza Strip the army could encounter unprecedented resistance from an army of fighters using guerrilla tactics, officials say.

The relatively high number of casualties Israel has suffered in its limited raids in Gaza over the past months — three soldiers killed and dozens injured — suggests Palestinian militants have developed new tactics and weapons.

Experts say the Israeli army will today have to face advanced anti-tank rockets, mine fields, ambushes, trenches and well-fortified positions commanded by trained militants.

A broad ground offensive now seems unavoidable as the army’s recent ground and air strikes have yielded little success in ending daily rocket fire against southern Israel from the densely-populated territory.

Israeli Defence Minister Ehud Barak warned on Tuesday that “every day that passes brings us closer to a broad operation in Gaza.

“We are not happy about it and we would be happy if circumstances would prevent it, but the day is definitely nearing,” the former army chief of staff said, a day after an Israeli soldier was killed in an incursion in southern Gaza.

But Prime Minister Ehud Olmert, who is engaged in intensive talks with Palestinian president Mahmud Abbas ahead of a peace conference expected next month in the United States, has so far been reluctant to give the green light.

“From a military point of view, every minute is a waste of time. But political considerations, such as the nearing international peace meeting in the US next month, are delaying it,” said reserve major general Jacob Amidror.

Olmert may also be holding off on a major operation because of the expected high toll the offensive would exact, as the premier’s public support plummeted following last year’s war against Hezbollah in Lebanon.

Top Israeli security officials warn that the Islamist Hamas movement, which violently seized control over Gaza last June, has built a formidable military based on Iranian know-how and tonnes of weapons smuggled in from Egypt.

“There is a process of production and arming of the Hamas. We are not ignoring it and it is felt on the ground. There are more weapons,” the army commander of the Gaza region, Brigadier Moshe Tamir told reporters on Monday.

The Israeli army’s total superiority in equipment, numbers and expertise could be diminished by some 8,000 Gaza militants employing guerrilla tactics, as Hezbollah did during the month-long war in 2006.

Anticipating an impending Israeli offensive with heavily armoured forces backed by tanks as well as extensive air raids, Hamas has in recent months put a major effort into strengthening its defences.

“Hamas are busy digging trenches, fortifications and tunnels. They have laid down mine fields,” the head of the Shin Beth internal security services Yuval Diskin told the parliament’s foreign affairs and defence committee on Monday.

Hamas has also created local weapon manufacturing workshops using over 70 tonnes of explosives smuggled in from Egypt as well as pipes and fertilizers which are often trucked in from Israel, Diskin said.

Hamas today has “a clear chain of command, and well trained regiments and brigades. They are developing their training programmes with activists who return from long training in Iran and other countries,” he added.

Israel’s last massive offensive in Gaza, triggered after militants abducted an Israeli soldier in a brazen cross-border raid near Gaza, cost the lives of over 400 Palestinians and three Israeli soldiers.

But the next offensive could exact a much higher toll on both sides, Amidror, the former head of the national security college, warned.

“The army will have to go in with much more force. The price will be paid by Gaza’s local population because Israel is preparing for war against a growing force that has sophisticated weapons and is well entrenched,” he told AFP.

“The Israel Defence Forces (army) will have to use more fire power and armoured vehicles that will cause much more casualties on the Palestinian side, but also on our side.”