Gen Kenneth McKenzie, the head of US Central Command, on Monday said Iran was the main and most challenging driver of instability in the Middle East.
Gen McKenzie told Washington's Middle East Institute think tank that challenges to US interests in the region included Iran, violent extremism, and the rising influence of Russia and China.
“For more than 40 years, the Iranian regime has funded and aggressively supported terrorism and defied international norms by conducting malign activities that destabilised not only the region, but global security and commerce as well," he said.
Gen McKenzie, in his first public remarks since President Joe Biden took office, said Iran, not ISIS or Al Qaeda, was "the major source of instability in Iraq and uses Iraq as a proxy battleground against the United States”.
But he said the US military presence in the Gulf region sent a signal to Iran, resulting in what he called contested deterrence.
“Our presence in the region, mostly defensive in nature, has brought us to a period of contested deterrence with Iran,” Gen McKenzie said.
“This presence sends a clear and unambiguous signal about our capabilities and will to defend partners and international interests, a signal that has been clearly received by the Iranian regime.”
On Yemen, Gen McKenzie said: "Our interest in Yemen is a counter-terrorism interest against Al Qaeda in the Arabian Peninsula and elements of ISIS there.
"American national interest begins and ends there. We are not a party to the Yemen civil war.”
He did not expect the recent decision by the Biden administration to halt offensive support to the Saudi-led coalition there to change the conflict.
“Our current support for the Saudi-led coalition has actually been extremely limited," Gen McKenzie said.
But he said Washington remained committed to supporting Saudi Arabia's efforts to defend itself from attacks by the Iran-backed Houthis in Yemen.
“Nothing that has been said or done means we are not going to continue to engage Saudi and our other coalition partners,” Gen McKenzie said.
He said that the defeat of ISIS in Iraq and Syria did not spell the end of the group.
"We must retain a vigilant focus on the mission, understanding that the territorial defeat of ISIS does not mean the organisation’s complete elimination,” Gen McKenzie said.
He estimated that US-backed local groups such as the Syrian Democratic Forces have detained about 10,000 ISIS fighters, including 2,000 foreigners.
The general also addressed of the proliferation drones across the region, calling it a "most concerning tactical development”.
“It’s a new component of warfare," Gen McKenzie said.
Russia’s and China’s rising influence in the region was also a challenge to the US, he said.
“Russia and China have exploited ongoing regional crises, financial and infrastructure needs, perception of declining US engagement and opportunities created by Covid-19 to advance their objectives.
“They are both vying for power and influence through a combination of diplomatic, military and economic means.”
On the current inclusion of Israel in Central Command’s orbit, Gen McKenzie, who was recently in that nation, hailed Arab-Israeli rapprochement through the Abraham Accords.
“The easing of tensions between Israel and Arab countries provides us with a strategic opportunity to align additional partners against shared threats to stability,” he said.
Gen McKenzie’s comments came as a senior British military commander in the Middle East described Iran as the greatest challenge to the Biden administration in the region.
Lt Gen Sir John Lorimer told The National on Monday that Mr Biden will face a major foreign policy test with Iran and said it remained crucial for the US to maintain its presence in the region.