A photo released by the Israeli army shows a missile on an intercepted ship in the Red Sea on March 5. The ship was carrying what Israel says was Iranian "advanced weaponry" bound for Palestinian militants in Gaza. (Ho/AFP/Getty Images)

The Israeli army said Wednesday that naval commandos intercepted a civilian vessel carrying a concealed Iranian shipment of arms to Palestinian militant groups based in the Gaza Strip.

The ship, the KLOS-C, was making its way up the Red Sea to Port Sudan when it was intercepted, Israeli officials said.

Prime Minister Benjamin Netanyahu said that the captured ship was “stocked with weapons destined for terrorist groups” and that “the entire operation . . . was organized by Iran.”

Sepah News, the official news agency of Iran’s Revolutionary Guard Corps, cited an informed but anonymous source within Iran’s military who denied the Israeli allegations, calling them “a baseless lie.”

In a dossier released to the news media, the Israeli army said that the shipment, which included Syrian-made M-302 surface-to-surface rockets, had been flown to Tehran from a weapons factory in Damascus and then transported overland to the Iranian port of Bandar Abbas on the Persian Gulf. After a stop in Iraq, the shipment had been making its way to Sudan’s main port, the army said. From there, it said, the shipment was likely destined to be moved by land through Sudan into Egypt and then to the Gaza Strip.

Although the army could not say how the rockets would have reached the blockaded territory, it released video footage and images of weapons in the ship. All of Gaza’s land crossings are blocked by Egypt in the south and Israel in the east.

“We don’t have the full plan yet, but we do know they were headed to Gaza,” said Lt. Col. Peter Lerner, an Israeli army spokesman.

He said that Israeli military intelligence had tracked the shipment for several months after it left Damascus and that the KLOS-C, a Panamanian-flagged vessel, was transporting rockets with a longer range than those Gaza currently possesses. Such rockets could strike targets almost anywhere in Israel.

The ship, with its cargo and 17 crew members of various nationalities, is en route to the Israeli port of Eilat and is expected to arrive in three days.

During a daily briefing, U.S. State Department spokeswoman Jen Psaki said she could confirm Israel’s assertion of having intercepted a shipment of illicit Iranian arms.

“The United States and Israel have had routine communication about this issue through intelligence and military channels as well as through our national security advisers,” Psaki said. She said she could not go into details but could confirm the ship’s existence, as well as some of the “details that the Israeli have put out there.”

Yuval Steinitz, Israel’s minister of intelligence and strategic affairs, who was in Washington on Wednesday, said that Israel had been tracking the ship “for some time” and that the Israeli military was given approval Tuesday to seize the ship in international waters. He declined to confirm the State Department’s assertion that the United States helped track the ship, saying only that intelligence cooperation between the two nations is “stronger than it has ever been.”

Steinitz described the intercepted rockets as “Syrian-assembled with Iranian ingredients and technology,” adding that while some Gaza-fired rockets have a similar range, the ones seized Wednesday carry a far heavier payload.

It is not the first time that Israel has claimed to have intercepted a weapons shipment from Iran. In 2011, Israeli commandos discovered 50 tons of concealed weaponry being transported from Syria to the Egyptian port of Alexandria. Two years earlier, the military uncovered 500 tons of Iranian-made weapons on a ship traveling to Latakia in Syria.

In a statement, Netanyahu, who is visiting the United States, accused Iran of concealing its true intentions and of “sending deadly weapons to terrorist organizations.”

“At a time when it is talking to the major powers, Iran smiles and says all sorts of nice things,” Netanyahu said. “The same Iran is sending deadly weapons to terrorist organizations and is doing so via a ramified network of secret operations in order to send rockets, missiles and other deadly weapons that will be used to harm innocent citizens.”

Netanyahu added: “This is the true Iran, and this state cannot possess nuclear weapons. We will continue to do whatever is necessary in order to defend Israel’s citizens.”

On Tuesday, Netanyahu addressed hundreds of Jewish American leaders at the annual conference in Washington of the American Israel Public Affairs Committee (AIPAC). During his address, he warned against trusting Iran on any level and on the issue of nuclear armament.

Jason Rezaian in Tehran and Scott Wilson in Washington contributed to this report.