An Iranian boat seized off the Yemeni coast was carrying sophisticated Chinese anti-aircraft missiles, a development that could signal an escalation of Iran's support to its Middle Eastern proxies, alarming other countries in the region and renewing a diplomatic challenge to the US.

Among the items aboard the dhow, according to a review of factory markings on the weapons and their packing crates, were 10 Chinese heat-seeking anti-aircraft missiles, most of them manufactured in 2005.

The missiles were labelled QW-1M and bore stencils suggesting they had been assembled at a factory represented by the state-owned China National Precision Machinery Import and Export Corporation, which is sanctioned by the US for transfers of missile technology to Pakistan and Iran.

The analysis of the weapons' markings and origins was based on photographs taken when Yemeni officials briefly displayed the weapons to journalists.

In 2008, late in the Bush administration, the US complained to China about two similar anti-aircraft missiles that were recovered from Shiite militants in Iraq, according to a diplomatic cable made public by WikiLeaks.