Former Secretary of State Mike Pompeo has come out against fellow Republican Dr. Mehmet Oz, claiming that the celebrity doctor cannot be easily trusted because of his ties to Turkey’s government.

This assertion came during a briefing by Pompeo, who served former President Donald Trump as CIA Director and as his top diplomat, to supporters of Oz rival David McCormick, a billionaire hedge fund CEO. Speaking at a press conference, Pompeo raised questions in particular about Oz's connections to Turkey's government through his vote in the 2018 Turkish general elections.

“We criticize American candidates all the time because they didn’t vote,” Pompeo said. “This is different from that. Not only did he not engage in the American [process] but he engaged in the Turkish political process. That raises in my mind a lot of judgments about his priority.”

ABC News was the first to report that Oz, who holds dual citizenship in the U.S. and Turkey, voted in that year’s Turkish elections. In a statement, Oz spokeswoman Brittany Yanick denied the vote should be considered "political involvement" and said Oz voted for a candidate opposed to Turkey's authoritarian President Recep Tayyip Erdogan.

At the briefing, Pompeo insisted that the question of whether Oz harbored any loyalty to Turkey was worth scrutinizing. It was possibly all innocuous, he conceded, but the former diplomat went on to caution that the cloud of suspicion was not to be dismissed.

Oz’s Turkish citizenship and business dealings in Turkey have been a subject of interest from the beginning of his candidacy. Beyond voting in an election, Oz also has a sponsorship deal with Turkish Airlines, the nation’s national flag carrier. He also is the owner of several properties in Turkey, including one that he loans out to the Turkish Ministry of Education.

However, Oz’s campaign vigorously disputed any characterization of the candidate as potentially disloyal to the U.S. In a statement, the campaign blasted McCormick for engaging in a “pathetic and xenophobic” attack on Oz.

Oz also has one particularly powerful backer in his corner who may not mind his ties to Turkey; former President Trump.

Last month, Trump announced that he would endorse Oz, citing his personal relationship with him and their shared background on television. The move was met with skepticism from those in Trump's orbit and other Republicans, but Trump has remained supportive of Oz and has committed to campaign on his behalf.

For his part, Trump also has done business in Turkey and his family has close connections with several prominent members of the Turkish elite. When in office, Trump frequently defended Turkey from critics within his own administration and he proudly touted his friendship with President Erdogan.