Saudi Arabia and Iran, which has been a staunch supporter of Yemen's Houthi rebels, agreed to normalise ties in a deal brokered by China this year. Since then, strides have been made towards peace in the eight-year conflict.
“The conflict [in Yemen] is more than just about Saudi Arabia and Iran,” said Mr Lenderking.
“There are internal divisions that have fuelled this conflict and have nothing to do with Saudi Arabia and Iran.”
He said that despite the rapprochement, Iran has continued to supply the Houthis with weapons and narcotics.
“I remain concerned about Iran's role,” he said.
His comments came hours after the US Coast Guard intercepted $80 million worth of heroin from a fishing vessel, the second such seizure this week. Both shipments had originated from the same port in Iran, US Central Command said.
Mr Lenderking had returned to the US from the Middle East after meeting senior Omani, Yemeni and Saudi officials.
During the talks, he emphasised the need for securing comprehensive agreements for peace, he said.
“This is the best opportunity for peace since the war began,” he said, adding that “great strides” had been made in the past year.
He said that despite a UN-brokered ceasefire that collapsed in October, Yemen remains in a ceasefire-like state, with no cross-border attacks into Saudi Arabia in the past year.
Mr Lenderking also noted the progress being made on the FSO Safer, a decaying oil tanker carrying 1.1 million barrels of oil that threaten to spill into the Red Sea in a catastrophe that would be bigger than the Exxon Valdez disaster.
He said a replacement crude carrier is in Djibouti, preparing for the next phase of the UN-operation to offload the oil and eventually remove the Safer from sea.
“We don't expect a durable solution, and we should not expect a solution to the eight-year conflict to happen overnight,” he said.
“A political process will take time and likely face numerous setbacks, but I remain optimistic that we have an opportunity for peace.”