WASHINGTON, July 18 - The power and sophistication of the missile and rocket arsenal that Hezbollah has used in recent days has caught the United States and Israel off guard, and officials in both countries are just now learning the extent to which the militant group has succeeded in getting weapons from Iran and Syria.
While the Bush administration has stated that cracking down on weapons proliferation is one of its top priorities, the arming of Hezbollah shows the blind spots of American and other Western intelligence services in assessing the threat, officials from across those governments said.
American and Israeli officials said the successful attack last Friday on an Israeli naval vessel was the strongest evidence to date of direct support by Iran to Hezbollah. The attack was carried out with a sophisticated antiship cruise missile, the C-802, an Iranian-made variant of the Chinese Silkworm, an American intelligence official said.
At the same time, American and Israeli officials cautioned that they had found no evidence that Iranian operatives working in Lebanon launched the antiship missile themselves.
But neither Jerusalem nor Washington had any idea that Hezbollah had such a missile in its arsenal, the officials said, adding that the Israeli ship had not even activated its missile defense system because intelligence assessments had not identified a threat from such a radar-guided cruise missile.
They said they had also been surprised by the advances that Hezbollah had made in improving what had been crude rockets - for example, attaching cluster bombs as warheads, or filling an explosive shell with ball bearings that have devastating effect.
The Bush administration has long sought to focus attention on Iranian missile proliferation, and regularly discusses with journalists intelligence evidence of those activities. But American officials in Washington made clear this week that they were reluctant to detail Iran's arming of Hezbollah in the current conflict.
The reason, according to officials across the government, was a desire by the Bush administration to contain the conflict to Israeli and Hezbollah forces, and not to enlarge the diplomatic tasks by making Iranian missile supplies, or even those of Syria, a central question for now.
Still, some officials in Washington admitted to being blindsided by the abilities of Hezbollah's arsenal.
"You have to acknowledge the obvious - we've seen a new capability in striking the naval vessel and in the number of casualties that have been sustained from the Hezbollah missile attacks," a Bush administration official said.
"In the past, we'd see three, four, maybe eight launches at any given time if Hezbollah was feeling feisty," the official added. "Now we see them arriving in large clusters, and with a range and even certain accuracy we have not seen in the past."
The officials interviewed agreed to discuss classified intelligence assessments about Hezbollah's capabilities only on condition of anonymity.
While Iranian missile supplies to Hezbollah, either by sea or overland via Syria, were well known, officials said the current conflict also indicated that some of the rockets in Hezbollah's arsenal - including a 220-millimeter rocket used in a deadly attack on a railway site in Haifa on Sunday - were built in Syria.
"The Israelis did forensics, and found several were Syrian-made," said David Schenker, who this spring became a senior fellow at the Washington Institute for Near East Policy after four years working on Middle East issues at the Pentagon. "Everybody recognizes that Syria has played an important role in facilitating transshipment - but not supplying their own missiles to Hezbollah."
Officials have since confirmed that the warhead on the Syrian rocket was filled with ball bearings - a method of destruction used frequently in suicide bombings but not in warhead technology.
"We've never seen anything like this," said one Western intelligence official, speaking about the warhead.
But it was Friday's successful launching of a C-802 cruise missile that most alarmed officials in Washington and Jerusalem.
Iran began buying dozens of those sophisticated antiship missiles from the Chinese during the 1990's, until the United States pressured Beijing to cease the sales.
Until Friday, however, Western intelligence services did not know that Iran had managed to ship C-802 missiles to Hezbollah.
Officials said it was likely that Iran trained Hezbollah fighters on how to successfully fire and guide the missiles, and that members of Iran's Al Quds force - the faction of the Revolutionary Guards that trains foreign forces - would not necessarily have to be on the scene to launch the C-802.
At the same time, some experts said Iran was not likely to deploy such a sophisticated weapon without also sending Revolutionary Guard crews with the expertise to fire the missile.
An administration official said intelligence reports have concluded that a small number of Iranians are currently operating in Lebanon, but the official declined to disclose their number or mission.