Israeli commandos seized a ship Wednesday that defense officials said was carrying hundreds of tons of weapons from Iran bound for Lebanon's Hezbollah guerrillas — the largest arms shipment Israel has ever commandeered.

The Israeli military said an Iranian document was found on board, showing that the arms shipment originated from Iran, although the paper was not shown to reporters. Rear Admiral Roni Ben-Yehuda, the deputy Israeli navy commander, said that despite its size, the shipment of weapons was "a drop in the ocean" of arms being shipped to Hezbollah.

"It's a cargo certificate that shows that it was from a port in Iran," military spokeswoman Lt. Col. Avital Leibovich said. "All the cargo certificates are stamped at the ports of origin, and this one was stamped at an Iranian port."

The Israelis boarded the ship before dawn in the waters near Cyprus. Israel has long accused Iran of arming its enemies.

Ben-Yehuda told a briefing that "hundreds of tons" of weapons were found on the ship, giving a much higher estimate than an earlier one of more than 60 tons.

Containers had Iranian shipping codes in English — "IRISL" on one side and "I.R. Iranian Shipping Lines Group" on the other. Some of the hundreds of crates lined up on the dock were open, revealing dark green missiles with English-language designations painted in black.

But hours after the seizure, Israel had not provided proof that the arms were meant for the Lebanese guerrillas.

Israeli military officials said the ship's journey started in Iran, and it arrived a week ago in Beirut. The next stop was Damietta, Egypt, where the weapons were loaded, they said. Ben Yehuda said the ship was headed for Latakia, Syria.

In Tehran, Syria's Foreign Minister Walid al-Moallem dismissed Israeli allegations the ship carried arms.

"Unfortunately, some official pirates in the seas, sometimes in the name of the navy, sometimes in the name of inspection, obstruct trade movement between Syria and Iran," al-Moallem said a joint news conference with his Iranian counterpart.

"This ship does not carry Iranian weapons to Syria and does not contain military material to manufacture weapons in Syria. This ship carries imported goods from Syria to Iran," al-Moallem added.

His comments made in Arabic were carried by Hezbollah's Al-Manar TV station and other Lebanese local stations.

It was unclear why al-Moallem said the ship was headed in the opposite direction of that claimed by Israel. Syrian officials were not immediately available for comment in Damascus.

Iran and Syria are close allies and Hezbollah's principal backers. Israel accuses Syria and Iran of supplying Hezbollah with weapons using air, sea and land routes — including through the port of Latakia.

If true, Israel's claim would bolster allegations that Syria has been complicit in getting weapons to Hezbollah.

An Egyptian government official said it was "illogical" to think that Egypt is shipping weapons to Hezbollah. The official, who would not be named because he was not authorized to discuss the case with the media, could not confirm or deny if the ship entered Egyptian ports. But he said it is not possible to search every ship that enters Egypt's ports.

Egypt's relations with Hezbollah have been strained following the arrest in April of 26 people suspected of working for the group. The group is on trial in Cairo accused of spying for a foreign group, planning attacks against tourists and shipping in the Suez Canal, and sending operatives to Gaza to help militant groups there.

In the southern port Israeli city of Ashdod where the ship was towed and docked, hundreds of rockets and piles of boxes of grenades were stacked on the shore as Israeli forces unloaded the cargo, a process that was expected to take hours.

Israel and Hezbollah fought a bitter war in the summer of 2006 that ended with a U.N.-brokered cease-fire and tesnions still remain high.

Wednesday's seizure was bigger than a similar haul in 2002, when Israeli military confiscated a vessel with 50 tons of missiles, mortars, rifles and ammunition headed for Palestinian militants in the Gaza Strip.

The presence of Iranian proxies in the Mideast have combined with worries over Tehran's nuclear program and arsenal of long-range missiles to make Iran the Jewish state's most formidable foe.

Israel shares the West's fears that Tehran is developing nuclear weapons, despite its assertions to the contrary. Neutralizing the Iranian nuclear threat remains Israeli Prime Minister Benjamin Netanyahu's top priority and Israel has not ruled out a military strike against Tehran's nuclear facilities.

Ben-Yehuda said weapons, including Katyusha rockets, were stashed on a commercial vessel operating under the guise of an aid ship, captained by a Pole and flying an Antiguan flag.

Based on intelligence reports, a naval unit patrolling the area intercepted and boarded the vessel without incident, defense officials said.

Deputy Defense Minister Matan Vilnai said the crew was not aware of the cargo's contents. The ship, the Francop, is operated by United Feeder Services, a Cyprus-based shipping company that said it picked up the cargo in Damietta, Egypt.

An employee of the company's chartering department who would not identify himself said the ship had been bound from Egypt to Cyprus and from there to Lebanon and Turkey. He said the company did not know what was inside the containers or where the cargo originated.

The employee asked that his name not be used because the company had yet to formulate an official response.

UFS' niche is bringing cargo to small ports not called by big container ships.

A senior Lebanese army official refused to comment on the Israeli report, saying it happened outside Lebanon's national waters. He spoke on condition of anonymity in line with military regulations.

A Hezbollah official, speaking on condition of anonymity because he did not want to speak publicly to the media, said the Islamist movement had no comment on Israel's claim.

Israeli Defense Minister Ehud Barak called the interception "another success against the relentless attempts to smuggle weapons to bolster terrorist elements threatening Israel's security." Netanyahu said the arms supply "was intended to hit Israeli cities."

The Lebanon-Israel border has been largely quiet since the 2006 Israel-Hezbollah war, although Israel has long warned that Hezbollah fighters have been rearming and now possess some 40,000 rockets.

Gaza militants also have dramatically reduced their rocket attacks on southern Israel since a bruising winter war. But militants continue to smuggle in rockets and components through underground tunnels with Egypt, the Israeli military says.

On Tuesday, the head of military intelligence said Gaza's militant Hamas rulers recently test-fired a missile capable of striking Israel's largest urban center, metropolitan Tel Aviv.

Eli Shaked, former Israeli ambassador to Egypt, said the growing arsenals of Hamas and Hezbollah are changing the balance of power between Israel and the Iranian-backed militant groups.

"The situation is becoming more and more complex because the weapons they are acquiring are more and more dangerous to civilian targets in Israel," Shaked said.