Trump has complained that McMaster, a three-star Army general, is too rigid and that his briefings go on too long and seem irrelevant, the Washington Post reported.
Speaking at the U.S. Holocaust Memorial Museum in Washington, McMaster said the U.S. would continue declassifying information that would shed light on Assad's war crimes.
"It is time for all nations to hold the Syrian regime and its sponsors accountable."
The Trump administration has a reputation for having a chaotic foreign policy, where one member of the band doesn’t seem to know what the other is doing.
US National Security Advisor H.R. McMaster is also expected to travel to Turkey in the coming days as part of a larger push by the Trump administration to rehabilitate ties with Ankara.
“This is a gift that gives over time” to Iran, McMaster said of the nuclear accord. “There’s the fundamental flaw of the sunset clause.”
At Rosh Hashana reception, Israeli ambassador lays out Jerusalem's expectations for the new year.
Mattis, McMaster and Tillerson present POTUS with new plan to curb the Islamic Republic's expanding reach.
‘I never heard national security adviser say anti-Israeli things’
US press reported earlier this week that Sheldon Adelson was distancing himself from a conservative campaign to cast McMaster as "deeply hostile" to Israel.