Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE fiercly defended the Trump administration's diplomacy efforts in a new op-ed, saying he is "proud" of the administration's progress despite "immense challenges."

“Over the past year, the United States has faced immense challenges in its dealings with North Korea, China and Russia, and in its efforts to defeat international terrorism,” he wrote Wednesday in The New York Times.

“But Americans should be encouraged by the progress the State Department and United States Agency for International Development have made in pushing for global peace and stability.”

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Tillerson pointed to sanctions on North Korea as an example of some of President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE's finest diplomatic work.

“Our peaceful pressure campaign has cut off roughly 90 percent of North Korea’s export revenue, much of which is used to fund illegal weapons development,” he wrote.

"We hope that this international isolation will pressure the regime into serious negotiations on the abandonment of its nuclear and ballistic missile programs. A door to dialogue remains open, but we have made it clear that the regime must earn its way back to the negotiating table. Until denuclearization occurs, the pressure will continue."

The White House has repeatedly demanded that North Korea give up their nuclear weapons before the U.S. is willing to come to the negotiating table, while Tillerson has voiced support for opening a dialogue with North Korea.

Tillerson also touted the “administration’s aggressive strategy to counter the Islamic State” as well as other terror-linked groups.

“As a result, the Global Coalition to Defeat ISIS has accelerated operations and has recaptured virtually all of previously held Islamic State territory in Iraq and Syria,” he wrote, while noting that this has cleared the way for “humanitarian aid and assistance” to get into such areas.

The op-ed comes as tensions between the White House and Tillerson have risen over the last few months, with the secretary of State's future in the administration being called into question.

Asked in a November interview on Fox News's "The Ingraham Angle" whether Tillerson would remain in the administration for the duration of Trump's first term in office, Trump replied: "We'll see."

"We'll see. I don't know who's going to be [at the State Department for the] duration," Trump said, noting that Tillerson is "doing the best he can" as the administration's top diplomat.

Tillerson's op-ed also comes after a handful of former State Department officials and lawmakers accused him of starving the agency of resources and weakening U.S. authority abroad.

"In spite of the challenges, I remain optimistic about the power of diplomacy to resolve conflicts and advance American interests," he concluded.