Israel's navy is casting its net wider and deeper in an effort to stop Gaza militants from receiving weapons by sea, a difficult mission made harder, Israel says, by political turmoil in Egypt and the Egyptian decision to fully reopen its border crossing with Gaza.

In recent weeks, Palestinian militants in Hamas-ruled Gaza have aimed rockets at Israeli cities, far enough away that Israel is convinced the projectiles came from abroad, probably Iran.

The first leg of a journey for weapons ending up in Gaza is a sea journey, ending with a trek across Egypt's barren Sinai desert, and then through a network of smuggling tunnels under the 9-mile (15-kilometer) Gaza-Egypt border.

The Israeli navy is trying to stop the shipments at their first stage — on the high seas.

Like other branches of Israel's military, the navy works mostly behind the scenes, and many of its operations are classified. They come to light when the navy carries out a major interception.

Its most recent success was March 15, when it seized the Victoria cargo ship. That weapons shipment departed from the Syrian port of Latakia and stopped in Mercin, Turkey. It was headed for the port of Alexandria in Egypt when it was intercepted, some 200 miles (320 kilometers) off Israel's Mediterranean coast. From there, Israel charges, the weapons were headed for Gaza.

The Israeli naval officer who commanded the raid said the main success was capturing Chinese-made C-704 missiles onboard that could have been "game changing" by allowing land-based forces to attack ships. As evidence of Iran's involvement, Israel produced Farsi instruction manuals, a booklet that identified the system by its Farsi name, Nasr, along with serial numbers and dates of issue in the Persian calendar.

Israeli defense officials believe Iran has since shifted its tactics, and now hides crates of weapons on civilian ships. In some cases, the crew isn't even aware.

The Israeli officials say Iran has a well-oiled mechanism of naval arms smuggling, with the primary route departing from the Iranian port of Bandar-Abbas and traveling through the port of Jebel Ali in Dubai and then via the Gulf of Aden to countries in east Africa. They are then believed to be shipped overland to Egypt, across the largely lawless Sinai peninsula and into Gaza through a vast network of tunnels under the short border.

Iranian Foreign Ministry officials refused to comment on the Israeli charges.

Israel has long accused Iran and Syria of using the seas to smuggle weapons to Hamas and to Hezbollah guerrillas in Lebanon. For this reason, Israel has maintained a strict naval blockade around Gaza since Hamas militants took control of the territory in 2007. Critics charge the blockade is illegal.

Israeli security officials believe that as Egypt prepares for elections, a power vacuum in the security establishment has led to "complete chaos" in Sinai that has hurt Israeli intelligence collection and left the Gaza border far more porous.

The problem becomes especially acute this Saturday as Egypt officially and fully reopens its passenger crossing with Gaza at the town of Rafah, after a long period of restrictions aimed at isolating the Hamas militant group that rules the Palestinian coastal strip.

So now, more than ever, Israel says it is trying to stop the weapons flow before they reach Sinai — by intercepting shipments on Mediterranean, Red Sea and Indian Ocean.

Experts also point to another problem: the sheer size of the seas. At any given moment, literally millions of containers are floating on the world's waterways.

"Without precise intelligence, it's like looking for a needle in a haystack," said Avraham Yassour, an Israeli expert in international maritime trade. He said it was impossible to say how many shipments have sneaked through, but it was fair to say that the ships Israel has seized are only a tiny fraction.

Israeli naval officials acknowledge that for each arms shipment they catch, others are likely getting through.

"The sea is very difficult," said a top Israeli navy officer. "Protecting a land border is relatively easy and you can protect the air with radars, but a maritime border is very soft."

He called the smuggling efforts "relentless" and said Israel is constantly scouring the seas in search of smugglers, declining to say whether any other arms busts have taken place. He spoke on condition of anonymity under standard military procedures.

Israel's naval activities have raised some legal questions about taking action beyond its territorial waters.

David Benjamin, a former high-ranking officer in the military's legal department, said maritime law entitles Israel to search any merchant vessel it believes is carrying contraband to support its enemies.

"The basis is that Israel is in an armed conflict with Hamas. Once you are in an armed conflict, it creates a legal framework in which you can operate," he said.

Scott L. Silliman, a military law expert at Duke University, agreed, though the situation is complicated because Hamas is an armed group, and not a sovereign state.

"That issue is quite similar to the state of armed conflict which the United States claims exists between itself and al-Qaida," he said. "I believe the consensus now is that an armed conflict can exist under these conditions."