The officials said that the intelligence is not definitive that the shipment has been sent, and that there is no evidence that the Chinese missiles have yet been used against American or Israeli forces during the conflict.

But even a debate in Beijing over sending missiles to Iran suggests the degree that China sees itself as having a stake in the conflict. Intelligence agencies have assessed that China is secretly taking an active stance in the war, allowing some companies to ship chemicals, fuel and components that can be used in military production to Iran for the war.

China has long been reluctant to send finished military equipment to Iran, but some officials in the government want Beijing to allow its companies to directly supply Iranian security forces during the conflict with the United States.

If the Chinese government did allow the shipment of missiles, it would be a significant escalation and an indication that at least some of China's leaders are working actively to bring about a US military defeat.

China is heavily dependent on oil that passes through the Strait of Hormuz, and is anxious not to do anything that extends the war, according to US officials. At the same time, at least some Chinese officials are interested in supporting Tehran in a war that is seen as weakening American standing and strength.

US officials have seen Russia as more eager to help Iran, sending food aid, nonlethal military supplies and satellite imagery. But Moscow appears to have ruled out providing any offensive or defensive military equipment, for fear of provoking the United States.

Chinese officials overall have been eager to protect, at least publicly, their image as a neutral party. A spokesperson for China's embassy to the United States strongly denied his government had shipped missiles to Iran during the war.

"China has never provided weapons to any party in the conflict; the information in question is untrue," said Liu Pengyu, the spokesperson.