MANAMA, Bahrain - American envoys challenged assertions Saturday that Washington seeks to diminish its role in Middle East affairs, insisting that U.S. political ties and energy needs bind the country closely to a region full of "threat and promise."

The defensive tone by U.S. officials, in response to questions raised at an international security summit in Bahrain, reflects growing speculation about a possible U.S. policy realignment toward Asia at the expense of Mideast initiatives.

Gulf Arab states, in particular, have urged the Obama administration to take stronger action on Syria, where Saudi Arabia and Qatar seek to open channels to send heavy weapons to rebel forces fighting to oust President Bashar al-Assad. The White House has favored a more cautious approach with the Syrian opposition, worried that hard-line Islamist rebel factions could be aided by stepped- up arms flow.

"The idea that the U.S. can pivot away from the Middle East is the height of foolishness," Sen. John McCain (R., Ariz.) said at the Bahrain gathering, which brings policymakers and political figures from around the world, including Iran and the Syrian opposition.

McCain, the ranking Republican member on the Senate Armed Services Committee, also said he believes there is a "steady increase" in fighters inspired by al-Qaeda joining the rebel side in Syria's civil war.

The comments followed a diplomatic flap after Bahrain's crown prince did not mention the United States at the opening of the conference Friday as he listed critical allies in the kingdom's 22-month battle against an Arab Spring-inspired uprising. Bahrain is home to the U.S. Navy's Fifth Fleet, which is the Pentagon's main counterweight in the region against Iran's military.

Many at the conference interpreted the crown prince's omission as a public slap against Washington for its criticism of Bahrain's crackdowns, including recent action such as banning opposition rallies and revoking citizenship for 31 activists.

More than 55 people have died in the unrest as the island nation's Shiite majority pushes for a greater political voice in the Sunni-ruled kingdom.

The head of the U.S. delegation, Deputy Secretary of State William Burns, said Washington's foreign policy objectives clearly include the "dynamic" rise of Asian economic and political power and "domestic renewal" to compete in the changing world economy.

"For all the logical focus on pivots in other directions, however, the fact remains that the United States cannot afford to neglect what's at stake in the Middle East," he said.

He credited Bahrain's leadership for some reforms aimed at easing tensions in the country, including giving more powers to the elected parliament. But he noted that "there is still a long road ahead" in following through on recommendations by an independent fact-finding committee last year, which included calls for investigation into allegations of high-level abuses against protesters.

The main Bahrain Shiite opposition group, Al Wefaq, said Saturday that it was open to the crown prince's offer for dialogue, but it was unclear whether any breakthroughs were possible. Past overtures have failed to gain traction.

Burns also said Middle Eastern oil remains crucial for the world economy despite projections of a sharp rise in U.S. crude output in coming years from techniques such as extracting oil from shale.

He pointed out, however, that other nations besides the United States need to help chart the region's course following the Arab Spring - suggesting no major unilateral push by Washington over Syria or other simmering disputes such as Iran's nuclear program.