WASHINGTON, June 6 (Reuters) - U.S. Defense Secretary Jim Mattis spoke on Tuesday by phone with his Qatari counterpart following a decision by Arab powers to cut ties to the Gulf ally, a Pentagon spokesman told Reuters, without disclosing the details of their discussion.

The Pentagon earlier on Tuesday renewed praise of Qatar for hosting a vital U.S. air base and for its "enduring commitment to regional security," sticking to a message of reassurance even as President Donald Trump, via Twitter, applauded Arab nations' decision to cut ties.

(Reporting by Phil Stewart; Editing by James Dalgleish) ((phillip.stewart@thomsonreuters.com; 1-202-898-8398; Reuters Messaging: phillip.stewart.thomsonreuters.com@reuters.net))