Hamas has smuggled a new arsenal into the Gaza Strip that would upset the balance of power, despite increased tensions between Cairo and the Islamic organization's allies Hezbollah and Iran, Israel believes.

Militants currently have 160 tunnels beneath the Sinai border that they are using to smuggle longer range rockets, anti-tank missiles and perhaps even anti-aircraft missiles, security sources say. Some of the tunnels are large and sturdy enough to let small all-terrain vehicles pass.

The Fatah-led Palestinian Authority, which severed ties with Hamas in 2006, believes Iran has smuggled a large number of weapons into Gaza by sea. Israeli officials, however, believe the bulk of arms are being brought through tunnels.

Iranian technology has been used to increase the range of Qassam rockets Hamas is producing in the Gaza Strip to more than 20 kilometers, they said.

Tensions between Cairo and Hamas allies have mounted since Egypt uncovered a spy network this month that was planning attacks on Israeli and foreign targets on Egyptian territory.

Still, Israeli officials believe Egypt has not managed to reduce the flow of arms into Gaza.

They said Egyptian soldiers' recent seizure of 900 kilograms of explosives at the Gaza border did little to stem the flow of weapons, and that Hamas was more interested in smuggling rockets and missiles.

Hamas has been studying its mistakes from Israel's Operation Cast Lead in Gaza. It failed to obtain its major objectives of abducting Israel Defense Forces soldiers, downing an Israel Air Force helicopter or seriously damaging an Israeli tank.

With the help of the Hezbollah, it has drawn up a new strategy of engagement with the IDF based on anti-aircraft and anti-tank missiles, instead of mining roads or booby-trapping houses.

Hamas is currently training units to operate its new missiles.

Israeli officials say Hamas military commanders have recognized that their militants' decision to take off their fatigues and don civilian clothing a few days into the fighting was a mistake. The Islamic group believes the decision damaged morale and was perceived by Gazans as indicative that they had lost control of the territory.

Hamas militants are now under orders to stay in uniform even if this makes them more easily targeted in Israeli air strikes.

Despite the increase in weapons entering Gaza, Palestinian militants have fired far fewer rockets at Israel over the past month. Israeli officials say Hamas is interested in reducing the number of retaliatory attacks against its tunnels in order to concentrate on stockpiling arms.

The Israel Air Force has not carried out an air strike against tunnels between the Gaza Strip and Egypt for more than a month.

The relative calm with Israel has led Hamas leaders to be less fearful of airborne assassination attempts. Last week, former Palestinian Authority prime minister Ismail Haniyeh and Mahmoud Zahar emerged from hiding to speak at an open rally in Gaza.

Both leaders had gone underground at the start of the Israeli incursion into the Gaza Strip. Israel has killed several Hamas leaders in air strikes, including Hamas cofounders Ahmed Yassin and Abdel Aziz Rantisi.