JERUSALEM — Palestinian Arab militants in the Gaza Strip are rearming and retraining for an imminent military showdown with the Israeli army, intelligence sources disclosed yesterday

The head of Israel’s intelligence service Shin Bet, Yuval Diskin, said 19 tons of explosives had been smuggled into Gaza in the past year. Other senior Israeli officials indicated that Palestinian Arab fighters were acquiring more effective weapons.

It is understood that Israel may use the unresolved kidnapping of a soldier in June as an excuse to renew major operations in Gaza to root out the new weapons threat.

Egyptian officials insisted yesterday that Hamas secure the release of Corporal Gilad Shalit or risk plunging Gaza into “crisis” and a renewed military incursion. Cairo has unsuccessfully tried to broker a deal trading Corporal Shalit for hundreds of Palestinian Arab prisoners in Israeli jails.

Corporal Shalit was captured by three militant groups and taken to Gaza, prompting a major Israeli incursion that was partially interrupted by the war in Lebanon.

Brigadier General Shalom Harari, a military intelligence officer, said Israeli forces might “go into Gaza in a big way” unless Corporal Shalit is freed. Accusing Iran of being behind the new weapons drive, he said Tehran had found willing partners in Palestinian Arab fighters.

“Iran is a Middle East superpower. For them, it is very important to get rockets into Gaza to develop a threat that surrounds Israel from all sides,” he said.

“Meanwhile, the war in Lebanon has renewed the will and added urgency to Palestinian efforts to upgrade their weapons systems.”

He said the arsenal at the disposal of the myriad militant groups in Gaza — which include Hamas, Islamic Jihad, the Al Aqsa Martyrs’ Brigade, and the Popular Resistance Committees — remained less powerful than that of the Lebanese group Hezbollah.

But he said the militant groups were exchanging home-made Qassam rockets for 122-milimeter Grad B missiles, which had a long enough range to hit the major southern Israeli city of Ashkelon.

While Palestinian Arab groups have boasted of a home-grown anti-tank missile known as the Batar, intelligence officials in Israel dismissed it. But they disclosed that militants have replaced the RPG-7, the standard rocket propelled grenade, with upgraded versions that can pierce Merkava tanks. “They want to bring in weapons that ‘break the equation’ of our military superiority,” one intelligence official said. “They want to be able to attack symbols of our power like the Merkava tank, the Apache helicopter, offshore missile boats, and armored bulldozers.”

In particular, the officials said, Palestinian Arab militants have a “real appetite” to adopt Hezbollah tactics from the war in Lebanon, when Russian-built Kornet missiles proved deadly against tanks on the battlefield while longer-range Katyushas were directed at towns inside Israel.

“The effort is to upgrade the rocket systems,” Brigadier General Harari said. But he added that while some weapons experts from Lebanon and Syria had been smuggled into Gaza, the Palestinian Arab groups were “not good at complicated weapons. You need courses to learn how to use them.”

In the Gaza refugee camp of Khan Younis, a Hamas member of parliament said yesterday that talk of Palestinian weapons improvements were lies. “This is a bunch of lies meant to justify Israel’s attacks on us,” Yehiya Musa said. “The situation in Gaza is the worst ever. Israel is the one threatening Gaza and attacking Gaza.”