White House national security advisor H.R. McMaster speaks to reporters in the White House briefing room in Washington, U.S., May 16, 2017. REUTERS/Joshua Roberts

TAORMINA, Italy (Reuters) - U.S. National Security Adviser H.R. McMaster said on Saturday that “of course” President Donald Trump backed NATO’s mutual defense doctrine, despite not making an explicit reference to it during a visit to Brussels this week.

Speaking at NATO headquarters earlier this week, Trump disappointed allies by not mentioning his support for Article 5, which states that an attack on one member of the alliance is viewed as an attack on all.

During his election campaign, Trump appeared to called Article 5 into question by suggesting that NATO members who did not pay their fair share for the alliance may not deserve to benefit from it.

“I think it’s extraordinary that there would be an expectation that the president would have to say explicitly that he supports Article 5. Of course he does,” McMaster told reporters at the end of a Group of Seven summit in Sicily.

“He did not make a decision not to say it,” McMaster continued. “It was implicit in the speech. There was no decision to not put it in there. It is a matter of fact that the United States, the president, stands firmly behind our Article 5 commitments under NATO.”