Israeli naval commandos intercepted a ship carrying "hundreds of tonnes" of arms from Iran to the Lebanese Hezbollah militia in a raid dozens of miles off its coast, officials said on Wednesday.
"We found dozens of containers, with hundreds of tonnes of arms bound for Hezbollah from Iran," deputy naval commander Rani Ben Yehuda told reporters, adding that the weapons included rockets, grenades and ammunition.
The shipment was among the largest ever seized by Israel, dwarfing the 50 tonnes of weapons found aboard the Karine A seized in 2002 on its way to Gaza, which dealt a major blow to relations between the Palestinians and Washington.
The military had earlier announced that it had seized the 137-metre (450-foot) Antigua-flagged vessel "Francop" before dawn around 100 nautical miles from the Israeli coast.
Israeli President Shimon Peres said that the ship appeared to be ferrying weapons to Hezbollah, and that the incident revealed "the huge gap between what Iran and Syria say and their actions."
Hezbollah declined to comment on the incident.
Israeli media reported that the vessel was carrying a shipment of several tonnes of anti-aircraft and anti-tank missiles, and Deputy Defence Minister Matan Vilnai told army radio that Katyusha rockets were among the cache.
Defence Minister Ehud Barak hailed the operation, calling it a "new success in our struggle against weapons smuggling aimed at reinforcing terrorist organisations that are threatening the security of Israel."
His remarks were carried in a defence ministry statement that said the ship was captured "near Cyprus," without elaborating on whether it was in Cypriot or international waters at the time.
Vilnai told army radio that the crew apparently did not know about the weapons, which were sealed in cargo containers.
Israel's Haaretz newspaper reported that the ship set out from Iran and later docked in Yemen and Sudan before passing through the Suez Canal en route to either Syria or Lebanon.
Israel has long accused arch-foes Syria and Iran of supplying weapons to Hezbollah and to Palestinian militants in the Gaza Strip, which has been ruled by the Islamist Hamas movement since June 2007.
On Tuesday, a senior Israeli general warned that Hamas had successfully test-fired out to sea a rocket that was capable of reaching Tel Aviv from Gaza.
The rocket, believed to be Iranian-made, has a range of about 60 kilometres (40 miles), putting Israel's major population centres in range, said Major General Amos Yadlin, head of military intelligence.
Hamas called the claim a "fabrication" designed to mobilise world opinion against the Islamist group before the UN General Assembly, which was on Wednesday due to discuss a report on the Gaza war that was deeply critical of both Israel and Hamas.
"This is a pre-emptive step by the Zionist enemy to influence international opinion," Hamas spokesman Fawzi Barhum said, adding that the report had put Israel in a state of "crisis."
The UN report by respected South African jurist and former international war crimes prosecutor Richard Goldstone accused both Israel and Palestinian militants of committing war crimes during the December-January Gaza war.
Some 1,400 Palestinians and 13 Israelis were killed in the three-week war launched by Israel on December 27 and aimed at halting rocket attacks, which have been mostly confined to communities a few kilometres (miles) from the Gaza border.
Israel has in the past seized shipments of weapons allegedly bound for Gaza, including in May 2003, when it intercepted a ship off its northern coast loaded with bomb-making material it said was from Hezbollah.
On January 3, 2002, at the height of the 2002 Palestinian uprising, Israel intercepted the Karine A in the Red Sea where it was bound for Gaza.
The late Palestinian leader Yasser Arafat admitted responsibility for the smuggling attempt, and the affair seriously eroded his standing with Washington.
In May 2001, the navy intercepted the Santorini, which was packed with 40 tonnes of arms sent to Gaza by a Palestinian faction based in Syria.