The retired Marine general who was tapped by the Trump administration to resolve a dispute with Qatar and develop what's been dubbed an “Arab NATO” has resigned from his position, Task & Purpose has confirmed.

The resignation was first reported by CBS News.

Gen. Anthony Zinni (Ret.) told Task & Purpose that he “just could not get the parties out there to engage in some sort of mediation process that we offered, and I felt that I couldn't do it much further.” He previously told CBS that regional leaders in the dispute between Qatar, Saudi Arabia and other Arab states were unwilling to agree to a “viable mediation effort” to resolve the ongoing spat.

Besides the Qatar issue, Zinni had also been tapped by then-Defense Secretary Jim Mattis to spearhead the Middle East Strategic Alliance — a security agreement for Arab states similar in design to NATO. The retired four-star general told Task & Purpose his role was to “get the concept rolling” and since there were now personnel at the National Security Council and Defense Department working on it, it no longer needed his involvement.

Zinni took the job of special envoy for the State Department at the request of Mattis — a long-time friend and fellow four-star general — and then-Secretary of State Rex Tillerson. Both have since exited the administration; Tillerson was fired and replaced with Mike Pompeo in March 2018, while Mattis resigned in protest in December.

When asked whether his resignation was connected to Mattis' resignation, Zinni said that he “was dissapointed by what happened, but it didn't really affect resignation.”

“Jim Mattis is a great friend of mine and he was the right guy for the job,” Zinni said, adding that, although Mattis first approached him to take the envoy role, Zinni had been getting “plenty of support from [Secretary of State] Mike Pompeo and [National Security Advisor] John Bolton.”

A former commander of U.S. Central Command, Zinni had previously served as a special envoy during the Bush administration to work on Israeli-Palestinian peace negotiations. He was offered the job of U.S. Ambassador to Iraq during the Obama administration but the offer was abruptly withdrawn without explanation.