JERUSALEM — Open crates from a cargo ship seized Wednesday by Israel revealed dark green missiles inside. Containers from the vessel bore writing in English that said "I.R. Iranian Shipping Lines Group."

Israel alleged that the shipment of hundreds of tons of rockets, missiles, mortars, grenades and anti-tank weapons — the largest it ever seized — was headed for Hezbollah guerrillas in Lebanon.

Israel stopped the ship, named the Francop, off the coast of Cyprus and towed it to the port of Ashdod. It carried orange, red, white and blue containers piled three deep on its deck.

Rows of crates from the vessel were displayed on the dock, and inside were rockets, hand grenades, mortars and ammunition. At least 3,000 missiles were on board, the Israeli military said.

The seizure spotlighted the dangerous tensions between Israel and Iran. Israel considers Iran a strategic threat because of its nuclear program and long-range missile development, dismissing Iranian denials that it is building nuclear weapons.

Among the weaponry displayed were Katyusha rockets. One of the long skinny missiles sat atop a pile of storage boxes the military had labeled in Hebrew "rocket 122 mm." The 122 mm Katyusha was the main weapon used against Israel by Hezbollah in a monthlong war in 2006. During that war, about 1,200 people were killed in Lebanon, most of them civilians, and about 160 people were killed in Israel.

Some of the weapons were hidden in the Francop's containers behind stacked bags of polyethylene labeled in English "NPC National Petrochemical Company," and the flame logo used by both the company and the Iranian Petroleum Ministry.

Israel said the huge weapons shipment backed up its long-standing contention that Iran is supplying large quantities of arms to Hezbollah and Hamas.

The Francop's containers were carefully unloaded on army forklifts to avoid accidental detonation. Some of the containers had the initials "I.R.I.S.L." printed on one side and the fuller title, "I.R. (Islamic Republic of) Iran Shipping Lines Group" on the other. Explosives experts and dog-sniffing units examined the haul.

The Israeli military said cargo certificates showed the ship departed an Iranian port for Syria, from where the weapons would be transferred to Hezbollah in Lebanon. The military did not show the documents, and Syria denied the vessel was carrying weapons.

Iran has never acknowledged giving weapons to Hezbollah. Proof of large-scale Iranian weapons shipments to its proxy forces on Israel's borders could reinforce the views of Israelis who favor their military making a pre-emptive strike against Iran's nuclear facilities.

The seizure may also complicate relations with Egypt, where Israel says the weapons were loaded.

Wednesday's dramatic operation allowed Israel to showcase its claims of weapons smuggling by Iran and Syria, which both nations have long denied. It also provided Israel with a chance to highlight what it considers Iranian mischief amid Western allegations that Tehran is developing nuclear weapons.

The seizure came a day after Israeli officials said Hamas tested an Iranian rocket that can hit metropolitan Tel Aviv — bringing to the fore Israeli fears that both Hezbollah and Hamas are rearming for more confrontations following the 2006 Lebanon war and last winter's Gaza war.