Pentagon chief comes up in support of NATO amid tensions

Acting U.S. Defense Secretary Patrick Shanahan said on Thursday that he backed a strong NATO, a move likely to calm allies nervous about Washington's commitment to the alliance after his predecessor resigned over differences with Trump.

"The United States is committed to NATO, our Article 5 obligations remain ironclad and America will continue to lead and support transatlantic unity (and) security," Shanahan told a news conference.

In his December resignation letter, Jim Mattis laid bare what he saw as an irreparable divide between himself and Trump and implicitly criticized the president for failing to value allies who have fought alongside the United States in several wars.