WASHINGTON, Sept 2 (Reuters) - President Barack Obama will assure Saudi King Salman of the US commitment to help counter any Iranian security threat, White House officials said on Wednesday, despite concern among Gulf allies that a new nuclear deal could empower Tehran in the region.Obama, hosting Salman on Friday on the king's first US visit since ascending to the throne in January, will seek to allay the fears of Washington's most important Arab partner that the lifting of sanctions on Iran would allow it to act in destabilizing ways.The White House talks will come less than two weeks before a possible US. congressional vote on the nuclear deal between six world powers and Iran, Riyadh's regional rival. The Obama administration wants to use the visit to shore up relations with Saudi Arabia after a period of tensions."We understand that Saudi Arabia has concerns about what Iran could do as their economy improves from sanctions relief," Ben Rhodes, Obama's deputy national security adviser, told reporters in previewing the visit.He said the United States believed Iran would use much of its assets, which will be unfrozen under the deal reached in July that also puts curbs on Tehran's nuclear program, to improve its battered economy.Rhodes acknowledged there was a risk that Tehran could spend those funds on "nefarious activities". But he said Obama would make clear the United States would do "everything that we can" to counter any Iranian threats to its neighbors.Gulf Sunni Arab leaders have accused Shi'ite Iran of fomenting sectarian violence in places like Yemen, Syria and Iraq. At the same time, some critics have blamed the Gulf states for contributing to the regional conflicts.Rhodes said Salman is expected during his visit to "express a comfort with the Iran deal as it relates to the nuclear issue" but reiterate other Saudi concerns about Tehran.