US Defence Secretary Jim Mattis warned Wednesday of Iranian efforts to create a Yemeni militia "in the image" of Lebanon's Hezbollah, after talks with officials in Saudi Arabia.
The kingdom leads an Arab coalition which for two years has been fighting in support of Yemen's government against rebels backed by Iran.
Saudi officials have accused Tehran and the Lebanese Shia militant group, which Iran supports, of aiding the Houthi rebels.
Mattis told reporters of the need to overcome Iran's efforts "in destabilising yet another country and create another militia in the image" of Hezbollah.
Washington alleges that Iran, Saudi Arabia's regional rival, has shipped missiles to Yemen but Tehran denies the charge.
A United Nations panel in January reported that it "has not seen sufficient evidence to confirm any direct large-scale supply of arms" from Iran.
Analysts from the International Crisis Group also said there has been "very little hard evidence" of Iranian arms to the Houthis, who are allied with troops loyal to former president Ali Abdullah Saleh.
Pentagon officials believe members of the Quds Force, the foreign operations wing of Iran's Revolutionary Guards, are in Yemen to help the Houthis.
Hezbollah, a powerful political movement in Lebanon, is fighting alongside government forces in Syria and has been declared a "terrorist organisation" by Riyadh.
Washington provides intelligence as well as aerial refuelling to coalition warplanes conducting air strikes in Yemen with American-supplied weapons.
But after talks with Saudi Arabia's King Salman and Defence Minister and Deputy Crown Prince Mohammed bin Salman, Mattis did not indicate if President Donald Trump's administration was considering an increase in that support.
Rights groups have repeatedly criticised the coalition bombing campaign in Yemen for causing civilian casualties.
"Our goal is to push this conflict into the UN brokered negotiations to ensure that it ends as soon as possible," Mattis told reporters on his first Middle East tour since taking office.
Seven ceasefires alongside UN-brokered peace efforts have so far failed to stop the fighting.