Israel said it intercepted a vessel yesterday carrying an Iranian shipment of advanced rockets bound for Palestinian militants, and said it proved Tehran could not be trusted in international nuclear talks.
The announcement came hours after Israel said it shot two Hezbollah fighters as they tried to plant a bomb near the Syrian-Israeli frontier.
Israel has long accused Iran and Syria of providing military aid to the Lebanon-based militant Shiite movement Hezbollah and to Palestinian militant groups, and the military spokesman's office tweeted that the ship was carrying weapons "capable of striking anywhere in Israel".
Iran's Al-Alam television channel quoted a military official as denying the Israeli report, calling it "without foundation".
Israel latched onto the weapons shipment to chide Western powers for negotiating with Iran over its nuclear programme.
"While Iran is conducting these talks, smiling to the international community, it continues to arm terrorist groups, continues to perpetrate terrorism around the world," Prime Minister Benjamin Netanyahu, currently in the United States, said.
The military said the Syrian-made weapons aboard the Klos-C were shipped overland to Iran and then onward towards Gaza by sea before being intercepted in the Red Sea between Sudan and Eritrea.
Lieutenant Colonel Peter Lerner said dozens of Syrian-made M302 surface-to-surface rockets were found aboard the ship.
Lerner said Israel had followed the shipment for "several months" and that the military knew "for a fact" the Iranians were behind it.
Militants in Gaza, which is governed by the Palestinian Islamist movement Hamas, have fired dozens of rockets at Israel since the beginning of the year, and Israel has responded with air strikes killing both militants and civilians.
Deputy defence minister Danny Danon said the shipment proved that world powers were wrong to grant Iran limited sanctions relief in return for it curbing or freezing its nuclear activities under an interim agreement clinched in November.
"It should now be clear to the international community that any easing of the sanctions against Iran will directly result in a strengthening of the terror organisations that operate under the auspices of the ayatollahs," he said.
Israel, the region's sole if undeclared nuclear-armed state, has long accused Iran of seeking to develop atomic weapons, charges vehemently denied by Tehran, which insists its nuclear programme is entirely peaceful.