Updated

Iran has been attempting to rearm the Lebanon-based terror network Hezbollah since the U.N.-backed cease-fire between Hezbollah and Israel took hold earlier this week, two U.S. officials told FOX News on Thursday.

A U.S. arms control official said it appears that Iran is using Syrian channels in its effort to give Hezbollah weapons it has used in the past, including Chinese-built C-802 radar-guided anti-ship missiles. Military observers said a C-802 was used successfully on an Israeli naval vessel off the coast of Tyre on July 14. The arms control officer and a senior American counterterrorism officer both said the U.S. government is "very concerned" about the "ongoing" effort.

Israel's Cabinet approved the U.N.-brokered cease-fire agreement Monday after 34 days of clashes across the Lebanon-Israeli border that began in response to Hezbollah kidnapping two Israeli soldiers in a cross-border raid and killing three others. Israel retaliated with air and ground strikes throughout Lebanon in an attempt to disarm the terror group, often taking criticism for causing civilian deaths. Hezbollah retaliated by firing 4,000 short- and mid-range rockets into northern Israel.

The cease-fire resolution authorizes up to 15,000 U.N. peacekeepers to deploy to southern Lebanon, a region the Shiite Muslim-rooted Hezbollah has controlled since Israel pulled back across the border in 2000. It also calls for the disarmament of Hezbollah and the unconditional return of the captured Israeli soldiers.

The counterterrorism official said the administration is "working with all of our allies" to get the message to Russia and China that they must do whatever they can to prevent their missiles from ending up in Lebanon.

A foreign government source told FOX News that the Chinese supplied Iran with at least 50 C-802s, and that the Iranians violated their contract with the Chinese by providing this weaponry to Hezbollah.

But the arms control officer was skeptical of that conclusion, saying, "Of course the Chinese knew" that Iran would turn over its weapons to Hezbollah, but Beijing doesn't care at all about nonproliferation.

"It's cash, and it's a lot of cash," the officer said, adding that while some members of the Bush administration have been willing to give the Chinese the benefit of the doubt and attribute the weapons proliferation to "bad export control," the geopolitical leanings of the Chinese have created the proliferation problem. The officials noted that none of China's weapons have inadvertently ended up in countries like India or Taiwan.

A leading security expert agreed with that conclusion.

"China understood that Iran was backing Hezbollah, they would have had to understood that in principal that if they transferred something to Iran, there's always a possibility that Iran was going to retransfer that Hezbollah," said John Pike, head of GlobalSecurity.org.

The arms control officer expressed optimism that an arms embargo in Lebanon could hold up in the short-term, but was less hopeful about the future.

"What happens in three months? If the will is there, the guns will get there," the officer said.

Also of concern is the prospect that Turkey, a Muslim ally in the War on Terror, is serving as or had been a point of access in the past for arms destined for Hezbollah. Pike said in recent days, Israelis have addressed their concerns directly to the Turks over the trans-shipment.

"They requested that Turkey detain a couple of airplanes coming into Lebanon from Iran. Turned out not to have weapons on them, but I don't think this is the last of it," Pike said. "Turkey has simply been looking the other way."

State Department spokesman Tom Casey said he was confident that if the situation in Turkey had been a problem, it isn't now.

"My understanding is that the issue of potential arms shipments through Turkey and through other countries are things that we have talked about with the Turkish government. ... We're fully convinced that they are taking and doing what would be necessary to prevent arms transfers from going through," Casey said.

FOX News' James Rosen contributed to this report.