Israeli forces have been astonished at the discovery of networks of bunkers and computerised weapons in Hizbullah positions, according to officials.

Troops have found air-conditioned bunkers 40 metres (125ft) below the ground and anti-tank weapons that originate in France, the US and Russia in southern Lebanon.

Many of the tactics and weapons employed by Hizbullah have neutralised Israel's military superiority and made a complete victory difficult to achieve.

Hizbullah's use of rockets to attack Israel was not unexpected but the Israeli armed forces have been repeatedly surprised since they went on the offensive a month ago.

The first major shock was when Hizbullah narrowly missed sinking an Israeli destroyer with a Chinese shore-to-sea missile. Four were killed in the attack.

"There were some weapons we did not know about," said General Ido Nehushtan. "There were others such as the unmanned aerial vehicles which we had detected before."

The revelations have increased since Israeli ground forces invaded southern Lebanon. "The main threat is the use of sophisticated anti-tank weapons against our armoured vehicles. One of the most effective is the Kornet which was supplied by Russia to Iran and then to Hizbullah," said Lieutenant Colonel Olivier Rafowicz.

"We have been very surprised by the quantity of weapons and the building that has been carried out in the last six years. We knew they were preparing for war but we did not realise to what extent."

Soldiers have discovered bunkers with listening and observation devices working in tandem with computers.

The bunkers meant that Hizbullah fighters could shelter from Israeli air and artillery bombardment and then surprise advancing Israeli forces. Often the bunkers were so well hidden that fighters could wait until the soldiers had passed and then attack them from behind.

Israel has so far lost more than 80 soldiers in combat. Its highly mobile armour and air support is less effective against guerilla fighters, and its armour has been neutralised by Hizbullah's acquisition of state of the art weapons.

Hizbullah's older anti-tank weapons have been effective against armoured personnel carriers and buildings used by soldiers for shelters. Its newer weapons such as the Russian Kornet and US TOW missiles have been highly effective succeeded in piercing the armour of Israel's main battle tank, the Merkava, reputedly one of the best-defended tanks in the world.

One member of an Israeli tank crew who had just left Lebanon told the Guardian: "It's terrible. You do not fight anti-tank teams with tanks. You use infantry supported by artillery and helicopters. Wide valleys without shelter are the wrong place to use tanks."

Although he said Hizbullah's weapons had been supplied by Iran, Lt Col Rafowicz admitted the militants' prowess also stemmed from its morale and organisation. They are very keen to engage our forces. They are not wearing suicide bomb belts but they are not afraid to die, which makes deterrence very difficult."

Gen Nehushtan said: "We have to recognise that we will be dealing with new definitions of victory. There will be no white flags being raised on this battlefield," he said.