Among the items aboard the dhow, according to a review of factory markings on weapons and their packing crates, were 10 Chinese heat-seeking antiaircraft missiles, most of them manufactured in 2005.
      
The missiles were labeled QW-1M and bore stencils suggesting that they had been assembled at a factory represented by the state-owned China National Precision Machinery Import and Export Corporation, sanctioned by the United States for transfers of missile technology to Pakistan and Iran.
The Chinese missiles were part of a larger shipment interdicted by American and Yemeni forces in January, which American and Yemeni officials say was intended for the Houthi rebels in northwestern Yemen. But the presence of the missiles in the seized contraband complicates an already politically delicate case.
      
The shipment, which officials portray as an attempt to introduce sophisticated new antiaircraft systems into the Arabian Peninsula, has raised concerns in Saudi Arabia, Oman and Yemen, as the weapons would have posed escalated risks to civilian and military aircraft alike.
      
And it has presented the Obama administration with a fresh example of Iran’s apparent transfer of modern missiles from China to insurgents in the larger regional contest between Sunni-led and Shiite-led states, in which the American military has often been entwined.
      
The United States has previously accused Iran, a Shiite-led theocracy, of sending weapons to the Houthis, who follow an offshoot of Shiite Islam. Saudi Arabia, an American ally, is considered the leading Sunni power in the region. Both sides have aided and equipped groups or governments they deem aligned with their interests, helping to fuel violence in Yemen, Iraq, Syria, Lebanon, the Palestinian territories, Sudan and elsewhere.
      
Iran has rejected the allegations as “baseless and absurd.” Neither the Iranian government nor the Chinese firm that markets QW missiles answered written requests for comment.
      
The government of Yemen has asked the United Nations to investigate the shipment and report the findings to the Security Council. Yemeni news media reported that United Nations experts were in Yemen last week.
      
The analysis of the weapons’ markings and origins was based on photographs taken when Yemeni officials briefly displayed the weapons to journalists.
      
Concerns over sophisticated Chinese missiles reaching Iran’s proxies have considerable regional history. They are part of both the larger worries over antiaircraft weapons set loose by conflicts across the Middle East in the past decade and the lingering frustration in Washington over China’s military aid to Iran.
      
In 2008, late in the Bush administration, the United States complained to China about two similar antiaircraft missiles that were recovered from Shiite militants in Iraq, according a diplomatic cable made public by WikiLeaks.
      
“We have demarched China repeatedly on its conventional arms transfers to Iran, urging Beijing to stop,” the cable noted.
      
The cable said the QW-1 missiles recovered in Iraq had been manufactured in China in 2003.
Like the American-made Stinger, China’s QW series is part of a class of weapons known as man-portable air-defense systems, or manpads. The cable instructed American diplomats to warn China of the “unacceptably high risk that any military equipment sold to Iran, especially weapons like manpads, that are highly sought-after by terrorists, will be diverted to nonstate actors who threaten U.S. and coalition forces in Iraq and Afghanistan as well as civilians across the region.”
      
The latest discovery of Chinese manpads came after the United States Navy detected the dhow, the Jeehan 1, as it took on cargo in an Iranian military-controlled port. The vessel then embarked on a high-seas smuggling run, according to accounts by Yemeni and American officials.
The vessel tied off on a pier in the harbor on Lesser Tunb Island, a tiny spit of land just west of the Strait of Hormuz that is claimed by both Iran and the United Arab Emirates, officials familiar with its voyage said. The island is occupied by Iran’s Revolutionary Guards.
      
After passing eastward through the strait and heading south along the Arabian Peninsula, the dhow was stopped on Jan. 23 by the American destroyer Farragut and a Yemeni boarding team off the coast of Al Ghaydah.
      
The dhow’s Iranian crew initially insisted the vessel was Panamanian-flagged and carried only fuel, an American official said. The military cargo, which included many ammunition crates that had been painted over with white or black paint, was found in hidden compartments, American officials said.
That cargo also included 316,000 cartridges for Kalashnikov rifles, nearly 63,000 cartridges for PK machine guns or the Dragunov series of sniper rifles, more than 12,000 cartridges for 12.7-millimeter DShK machine guns and 95 RPG-7 launchers.
      
The rifle cartridges were packaged in crates strongly resembling packaging used by Iran’s Defense Industries Organization, another firm under American sanction, according to James Bevan, director of Conflict Armament Research, a private arms-tracking firm that has documented the spread of Iranian ammunition in East and West Africa.
      
The vessel also carried 10 SA-7 shoulder-fired antiaircraft missiles with two gripstocks for firing them, nearly 17,000 blocks of Iranian-made C-4 plastic explosives, 48 Russian PN-14K night vision goggles, and 10 LH80A laser range finders made, according to their placards, by the state-run Iran Electronics Industries, also under American sanction.
      
The original provenance of the SA-7s was not clear, though the crates they were in had stenciling in Bulgarian.
      
The captain and crew of the Jeehan 1 remain in Yemeni detention, and the dhow has been impounded under Yemeni custody, a Yememi official said.
      
An American official called the shipment “deeply disturbing” and said it “clearly appeared to violate” Security Council resolutions prohibiting Iran from exporting arms.
      
Two independent arms-trafficking researchers who have reviewed photographs and written a summary of the markings on the missiles and crates said the weapons appeared to be of Chinese origin.
      
Matthew Schroeder, an analyst for the Federation of American Scientists in Washington and the Small Arms Survey in Geneva, said that this was the first time to his knowledge that the QW-1M had left state control.
      
“If so, and these missiles were indeed bound for insurgents, this shipment is extremely worrisome, both from a regional security and a global counterterrorism perspective,” he said.
      
Unlike many older shoulder-fired antiaircraft missiles seen in insurgent hands around the world, the QW-1M is believed by analysts to have a seeker head more resistant to countermeasures intended to deceive it.