WASHINGTON (Reuters) - The United States and six Gulf nations have targeted 13 individuals they say are al Qaeda and Islamic State militants, in an action intended to disrupt terrorism financing in Yemen, U.S. administration officials said on Wednesday.

Among those targeted are the militant group’s chief financial officer in Yemen and head of assassinations in that country. The action puts those named on a business blacklist, which prohibits any financial actions and freezes their bank accounts.

The nations joining the United States in the sanctions were Saudi Arabia, the United Arab Emirates (UAE), Bahrain, Oman, Kuwait and Qatar.

“This is the largest ever multilateral designation in the Middle East,” U.S. Treasury Secretary Steven Mnuchin said in Riyadh on Wednesday.

U.S. administration officials said this is the first joint sanctions action by Washington and Gulf states. The coordination was particularly significant because of a months-long diplomatic crisis between Qatar and several Gulf states.

Saudi Arabia, Egypt, the UAE and Bahrain severed relations with Qatar in June, accusing it of financing terrorism, meddling in the affairs of Arab countries and cozying up to their arch-rival Iran.

The four countries have since added dozens of individuals and entities to a blacklist they say are associated with Qatar.

One of the individuals on Wednesday’s sanctions list, Abdula Wahaba al-Humayqani, and one of the entities, Rahmah Charitable, are part of that blacklist.

Qatar’s National Counter Terrorism Committee said in a statement it had strengthened its anti-terrorism finance laws.

Qatar is “committed to taking the necessary steps to defeat terrorism in all its forms, and will continue to work closely with the United States to impose sanctions on those who facilitate terrorist activity,” Major General Abdulaziz A. Al Ansari said in the statement.

Qatar signed an agreement with the United States in July to increase cooperation on fighting terrorism finance, Qatar’s counter-terrorism committee said.

Peter Harrell a sanctions expert at the Center for a New American Security, said cooperation between Gulf nations and Qatar was an important step.

“Qatar has had a history of not being as robust on terrorism finance,” Harrell said. “It’s heartening to see Qatar do this. It signals some ability to cooperate.”