The United States warned Saturday it was capable of deploying "overwhelming force" in the Middle East as it faced questions about its willingness to use its military power in the region.
Defense Secretary Lloyd Austin told the Manama Dialogue in Bahrain's capital that all options would be open if diplomacy fails to halt Iran's nuclear programme, but he was also forced to rebut claims the US has become reluctant to use force.
The Pentagon chief was asked why Washington did not respond to last month's drone-and-artillery attack on a base used by the US-led coalition fighting the Islamic State group in Syria.
"The United States of America maintains the right to defend itself. And we will defend ourselves and our interests, no matter what, at the time and place of our choosing," he replied.
"And let no country, let no individual be mistaken about that. We are committed to defending ourselves and our interests and that includes our partners as well," said Austin.
"And we're also committed to not allowing Iran to get a nuclear weapon."
Iran and world powers are set for talks on November 29 aimed at reviving an accord that placed restrictions on its nuclear programme in exchange for sanctions relief. Tehran has always denied it is seeking nuclear weapons.
Austin said Washington's major goal was to strengthen its "unmatched" alliances in the Middle East, but said military force remained an option with tens of thousands of its troops stationed in the region.
After ending its 20-year occupation of Afghanistan in August, the US is poised to withdraw its combat troops from Iraq by the end of the year.
This month, Iraq's prime minister escaped an assassination attempt two days after security forces clashed with supporters of Iran-backed parties that lost support in recent elections.
- 'Strong and sure' -
On Saturday, Iran said it had seized a foreign boat smuggling diesel in the oil-rich Gulf.
Since February, Iran and Israel have been engaged in a "shadow war" in which vessels linked to each country have come under attack in waters around the Gulf.
The US and Israel accuse Iran of using drones and missiles to destabilise the region.
In brief remarks to the forum, senior Saudi figure Turki bin Faisal Al Saud called for "demonstrative action" in the region, including the "total enforcement" of the arms embargo on Yemen's Iran-supported Huthi rebels, who are fighting a Saudi-led coalition.
Austin said that "America's commitment to security in the Middle East is strong and sure."
"Ultimately, our mission is to support diplomacy and to deter conflict and to defend the United States and our vital interests," he said. "If we're forced to turn back aggression, we will win and we will win decisively."
Austin's visit comes days before Iran returns to talks with world powers on resuming a nuclear deal which has been stalled since 2018, when former US president Donald Trump walked away.
On Friday, US special envoy Robert Malley told the conference that time was running out to return to the deal if Iran continues to make "advances" in its nuclear programme.
"We remain committed to a diplomatic outcome of the nuclear issue," Austin said. "But if Iran is not willing to engage seriously, then we will look at all the options necessary to keep them the United States secure."
Iran's Gulf neighbours are concerned that concessions could be made to the Islamic republic in the nuclear talks.