And he pointed to the ongoing plan to destroy Syria's chemical weapons as diplomacy made possible by America's military threat. He said President Barack Obama's threat to strike Syria after a chemical weapons attack believed to be the work of Bashar Assad's government led to the ultimate deal to remove and destroy the arsenal.
But Hagel argued that the emphasis on diplomacy must not be misinterpreted.
"We know diplomacy cannot operate in a vacuum," Hagel said. "Our success will continue to hinge on America's military power, and the credibility of our assurances to our allies and partners in the Middle East that we will use it."
And, he warned that with America's sophisticated weapons, "no target is beyond our reach."
As part of the security effort, he said the U.S. wants to take steps to beef up the Gulf region's ability to defense itself.
Washington has pushed for more than 20 years, particularly after Iraq's invasion of Kuwait in 1990, for better defenses among a group of Gulf nations that includes long-time allies Saudi Arabia and Bahrain. The latter hosts the U.S. Navy's 5th Fleet. Progress has been limited, in part because of their reluctance to collaborate.
Hagel's speech continued a theme he has repeated over the past two days in private meetings with Gulf leaders and in remarks to troops aboard the Navy's USS Ponce warship at the nearby U.S. base. He is countering apprehension in the region that the Iran nuclear deal, coupled with U.S. budget pressures and the drawdown in Afghanistan, could signal a decline in America's commitment to the region.
The interim Iran agreement carved out less than two weeks ago by major nations, including the U.S., would freeze parts of Iran's nuclear program in exchange for some relief from crippling Western economic sanctions. The deal may open the door to warmer relations with the West, but it has escalated tensions in the Gulf region, where leaders worry that it could embolden Iran and destabilize the area.
Hagel was speaking at an annual international security forum known as the Manama Dialogue, just across the water from Iran. His broader message was that while Iran's nuclear program is a critical worry, its other conventional missile threats, terrorism links and occasional provocative maritime behavior also greatly concern the U.S. and the region. And those threats are not addressed by the nuclear agreement.
Hagel was challenged at one point during a question-and-answer session by a former Iranian nuclear negotiator over why his address failed to mention Israel's possession of nuclear weapons. Hossein Mousavian, who is now a scholar at Princeton's Woodrow Wilson School of Public and International Affairs, told Hagel he "didn't mention a single word about the major threat of nuclear bombs in the region, which is Israel."
Hagel replied by noting that Iran is in violation of "many United Nations resolutions."
Israel is widely understood to possess nuclear weapons but declines to confirm it.
Hagel spent a chunk of the speech detailing the strength of the U.S. military in the area, including more than 35,000 air, land and sea forces in and immediately around the Gulf. They include about 10,000 Army troops, advanced jet fighters, more than 40 ships, sophisticated surveillance and intelligence systems, and a broad missile defense umbrella made up of ships, Patriot missile batteries and radars.
The most concrete proposal Hagel outlined is the Pentagon's plan to allow military sales to the Gulf Cooperation Council, so the six-member nations can have more coordinated radars, sensors and early warning missile defense systems. While the U.S. can sell to the individual nations, Hagel is arguing that selling the systems to the GCC will ensure that the countries will be able to communicate and coordinate better.
It is unclear, however, how effective that plan will be considering it can be difficult for the six sometimes-combative nations of the GCC Saudi Arabia, Kuwait, Bahrain, Qatar, the United Arab Emirates and Oman to reach agreements.
Hagel also said he wants the Gulf nations to participate in an annual defense ministers' conference, and would like the first meeting to happen in the next six months.
Hagel is expected to visit Qatar and Saudi Arabia to meet with leaders in the coming days.
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Associated Press writer Adam Schreck contributed to this report.