WASHINGTON (Reuters) - The chairman of the U.S. Senate Foreign Relations Committee said on Monday he would block arms sales to Saudi Arabia, the United Arab Emirates and other members of the Gulf Cooperation Council pending progress in resolving a simmering dispute with Qatar. “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 ISIS and counter Iran,” Republican Senator Bob 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 United Arab Emirates imposed a boycott on Qatar, their tiny but wealthy neighbor, on June 5, accusing it of supporting terrorism. They have sent it 13 demands including closing al Jazeera television, curbing relations with Iran, and paying reparations. Under U.S. law, major foreign U.S. arms sales are submitted for review to a small group of lawmakers, 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 U.S. 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 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 United States. 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 $350 billion 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,” Corker wrote. 