Chuck Hagel, US defense secretary, has opened the door to more advanced weapons sales to the Gulf states as Washington seeks to convince regional allies of its strategic commitment amid progress in the Iran nuclear talks.
The US would place "even more emphasis on building the capacity of our partners in order to complement our strong military presence in the region," Mr Hagel told delegates at a regional security conference in Bahrain.
He proposed allowing the Gulf Cooperation Council to acquire weapons systems collectively, rather than as individual customers, "including items for ballistic missile defense, maritime security and counter-terrorism".
Gulf powers are privately fuming about the rapid pace of negotiations between global powers and Iran over limiting the Islamic republic's nuclear program in return for sanctions relief.
Many GCC leaders worry that the US has been duped into a dangerous deal that will allow Iran, their historic regional competitor, to develop nuclear weapons.
They also fear the US, enjoying growing domestic oil production, is abandoning its long-term strategic partnership with the oil-rich GCC states in return for progress on an Iranian nuclear deal.
Mr Hagel, building on previous diplomatic efforts led by John Kerry, US secretary of state, sought to reassure his GCC allies.
"I am under no illusions, like all of you, about the daily threats facing this region, or the current anxieties that I know exist here in the Gulf," Mr Hagel said.
"These anxieties have emerged as the United States pursues diplomatic openings on some of the region's most difficult problems and most complex issues, including Iran's nuclear program and the conflict in Syria."
The US stance on rejecting military action against the regime in Syria has reaffirmed Arab concerns that Washington is realigning its foreign policy objectives as it rebalances its strategic priorities towards eastern Asia.
"We will continue to work with partners throughout the region to help bring about a political settlement to end this conflict," Mr Hagel said. But he also called for efforts to ensure that aid to the opposition did not "fall into the wrong hands".
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Concerns have been growing that money pouring into Syria from the Gulf is helping boost Islamist extremist groups fighting the regime of Bashar al-Assad.
Mr Hagel, who has also been holding bilateral meetings with regional leaders, sought to reassure opinion-makers that the US was not retreating.
"As America emerges from a long period of war [in Afghanistan], it will not shirk its responsibilities," Mr Hagel said. "America's commitment to this region is proven. And it is enduring."
He said the US has more than 35,000 military personnel in and around the Gulf, including 10,000 soldiers, the deployment of the US' most advanced aircraft and 40 US navy vessels patrolling nearby waters.
The US proposal to deliver more advanced defense systems to the Gulf comes as its leading power, Saudi Arabia, seeks to build a closer union within the GCC.
Closer political and defense union has been on the agenda since the regional revolutions of 2011 spread into the Gulf, notably Bahrain, where the majority Shia rose up against the minority Sunni led government.
Reflecting concerns among some GCC states about a Saudi-led regional grouping, Oman's foreign minister at the conference said the sultanate opposes upgrading the GCC to a union.
Yusuf bin Ali said Oman, a backchannel conduit for contacts between Washington and Tehran, would not prevent a union but would not join.