The Palestinian militant group Islamic Jihad, which traded deadly fire with Israel at the weekend in Gaza, does not expect a subsequent truce to last long and has at least 8,000 fighters ready for war, a spokesman said.

Islamic Jihad is the second largest armed group in Gaza, after Hamas, which rules the tiny Mediterranean enclave. The two share a commitment to the destruction of Israel and both are classified as terrorist groups by most Western governments.

However, while Hamas has recently spent much of its energy on the business of government, Islamic Jihad has kept its focus firmly on the conflict, gaining in prominence and enjoying significant backing from Muslim supporters, including Iran.

"We are proud and honoured to say that the Islamic Republic of Iran gives us support and help," Abu Ahmed, the spokesman for Islamic Jihad's armed wing, the Jerusalem Brigades, told Reuters in a rare, long interview.

He denied widespread reports that Iran had provided his group with arms and smiled at suggestions it now receives more sophisticated weaponry from Tehran than Hamas. He also declined to comment on rumours that the Jihadists were trained by Iran.

"What I will say is that we have every right to turn to every source of power for help," said the burly, bearded Abu Ahmed, occasionally flicking a string of yellow prayer beads.

Islamic Jihad's latest confrontation with Israel left 12 Palestinian gunmen and one Israeli civilian dead. The fighting ended only after neighbouring Egypt brokered a ceasefire with both parties, but Abu Ahmed did not see it lasting long.

"Theoretically the calm has been restored, but in practice it hasn't really," he said. Israel, he said, is itching for a fight in Gaza following last month's prisoner-swap accord, in which Israel released 477 Palestinian prisoners in exchange for Gilad Shalit, an Israeli soldier held by Hamas since 2006.

Israel says it attacks only in self-defence.

TRADING BLOWS

It killed five senior Islamic Jihad militants on Saturday in retaliation for a rocket attack two days earlier that it blamed on the group. That rocket caused no casualties, but landed deep enough into Israel to set off sirens on Tel Aviv's outskirts.

Abu Ahmed denied responsibility for the missile, saying this was how Israel had managed to find five top fighters together in the open -- because they had not expected to be targeted.

But the Jerusalem Brigades soon hit back, firing numerous rockets into southern Israel, piercing the country's defensive missile shield. One Israeli man died, at least four others were injured, while cars and a building were also set ablaze.

The group posted a video online showing a missile-launcher on the back of a truck firing a salvo of rockets. It was the first time the group has claimed to have such firepower, although there was no independent confirmation of its use.

"The Jerusalem Brigades really surprised Israel, forcing them to rethink their assessment of us ... I don't think they realised we had that weaponry," said Abu Ahmed, indicating the vehicle was immediately hidden underground after the attack.

Jerusalem Brigades cells are dotted around Gaza and Abu Ahmed said there was huge demand from youngsters to join.

"We take some, but can't accept everyone ... It is a question of quality, not quantity," he said, giving for the first time an estimate of the strength of the force. "We have at least 8,000 fighters, who are fully equipped."

The group got a boost to its standing in August when the new rulers in Egypt started dealing with it directly over truces, rather than through Hamas. Abu Ahmed said Hamas was not involved in the latest fighting and that all the talking was with Egypt.

He played down reports of tensions with Hamas, which since Israel's military offensive in Gaza in late 2008 has appeared reluctant to go head-to-head with its sworn enemy.

"Certainly in terms of ideology, there is no difference between Hamas and the Islamic Jihad. The difference is in the methodology," Abu Ahmed said, adding that Hamas's governmental role meant that it was "more vulnerable to outside pressure".

He said Islamic Jihad's biggest problem was the Israeli armed drones that regularly buzz over Gaza seeking out militants. "Warfare has changed. You can't just hide a gun in your jacket like you could in the 1980s," he said, adding that the Jihadist fighters were not afraid of sudden death.

"It is a good feeling to be under drone attack. When we chose the path of resistance, we opted either for martyrdom or victory. Martyrdom is the more desirable."