Washington (CNN) President Donald Trump's personal lawyer held a back channel phone call with Venezuela's embattled President Nicolas Maduro in September 2018, according to The Washington Post, serving as the latest example of the scope of Rudy Giuliani's role in US foreign diplomacy.

People familiar with the effort told the Post that Giuliani and then-Rep. Pete Sessions of Texas participated in the phone call with Maduro in a diplomatic endeavor to ease him from power and reopen Venezuela to business. Sessions' spokesman Matt Mackowiak told the newspaper in an article published Sunday that the call was a followup to a meeting Sessions had with Maduro in Venezuela that spring.

Upon learning of the call, White House officials did not know why Giuliani was involved, a former senior administration official told the Post.

The former New York City mayor's call with Maduro in late 2018 ran counter to White House's increasingly hardline approach to Venezuela at the time. Giuliani met then-national security adviser John Bolton around the time of the call to discuss a plan to ease Maduro from power, two people familiar with the meeting told the Post, but Bolton rejected the idea.

The Post's Sunday article builds on previous reporting from the newspaper that Giuliani had entered an agreement to find a way to negotiate a back channel communication between Trump and Maduro.

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