Threat from Bob Corker, chairman of foreign relations committee, comes after Trump announced Saudi arms deal and plan to create 'Arab Nato'
A senior Republican senator has threatened to block arms sales to Saudi Arabia, the UAE and other Gulf states until a diplomatic dispute with Qatar is resolved.
The threat by Bob Corker, who is chair of the Senate foreign relations committee, comes after Donald Trump used a trip to Saudi Arabia to announce plans to unveil one of the largest arms deals in US history worth up to $128bn.
"All countries in the region need to do more to combat terrorism, but recent disputes among the GCC countries only serve to hurt efforts to fight IS and counter Iran," Corker wrote in a letter to Secretary of State Rex Tillerson.
His action could increase pressure on members of the Gulf Cooperation Council to settle the crisis. The GCC groups Saudi Arabia, Kuwait, United Arab Emirates, Qatar, Bahrain and Oman.
Saudi Arabia, Egypt, Bahrain and the UAE imposed a boycott on Qatar on 5 June, accusing it of supporting terrorism.
They have sent it 13 demands which included proposals to curb relations with Iran and paying reparations.
The demands also included calls for the closure of Al Jazeera, Middle East Eye and other media outlets they claim are supported by Doha.
Arms sales to Saudi
Under US law, major foreign US arms sales are submitted for review to a small group of politicians, including the chairman of the foreign relations committee, before they can go ahead.
Trump considered Corker as a potential vice president and secretary of state, and he works closely with the White House. The administration would be unlikely to ignore his resistance to the arms sales, and US officials said they considered his statement part of a broader effort to solve the Qatar crisis.
A state department official noted that Tillerson called on Sunday for the countries involved to sit down together and discuss ways forward.
The official declined to comment on arms sales beyond saying the department remains committed to working with lawmakers.
It was not immediately clear what sales would be affected. Trump has announced billions of dollars in arms sales since taking office in January. He sees weapons sales as a way to create jobs in the US.
The Saudi crown prince, Mohammed bin Salman, began negotiations on this deal shortly after the 2016 US election when he sent a delegation to Trump Tower to meet the president's son-in-law, Jared Kushner, who is a senior adviser to the president.
The deal was described by the Trump administration as being a cornerstone towards encouraging the Gulf states to form its own military alliance, which it dubbed the "Arab Nato".
The White House said the president hoped the military alliance will fight terrorism and keep Iran in check.
A Corker aide said his action would not affect sales that had already been reviewed by Congress or non-lethal assistance, including training.
One sale already cleared by Congress was for up to $350m in precision-guided munitions and other offensive weapons to Saudi Arabia.
In his letter, Corker said he was pleased with Trump's recent trip to Saudi Arabia, which included a GCC summit.
"Unfortunately, the GCC did not take advantage of the summit and instead chose to devolve into conflict," he said.