Sen. John McCain John Sidney McCainThe electoral reality that the media ignores Kelly's lead widens to 10 points in Arizona Senate race: poll COVID response shows a way forward on private gun sale checks MORE (R-Ariz.) is calling on President Trump to fill senior State Department posts that have remained vacant more than two months into his presidency.

Speaking at a forum in Brussels on Saturday, McCain said it was essential to appoint senior officials to provide support for Secretary of State Rex Tillerson, The Associated Press reported.

"[Tillerson] doesn't have a team there at the State Department," McCain said. "And I think it's incumbent for the president and the administration to get people nominated and confirmed."

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The State Department's two deputy-level posts remain unfilled, and the president's budget proposal released earlier this month calls for deep cuts to the department, while bolstering defense and homeland security spending.

McCain on Saturday pointed to "confusion" over Tillerson's attendance at a NATO meeting of foreign ministers.

The meeting was originally set for early April, and Tillerson said that he would not attend in order to be in the U.S. for a visit with Chinese President Xi Jinping. He is set to visit Moscow later on in the month.

The meeting was eventually rescheduled to take place at the end of March, and Tillerson is now expected to attend following criticism over his initial decision to skip the meeting.