Kiev, Ukraine — U.S. Secretary of State Mike Pompeo met Ukraine's leader Friday on his first trip to the country at the heart of President Trump's impeachment trial as America's top diplomat. Pompeo met President Volodymyr Zelensky, who is at the center of Mr. Trump's historic impeachment trial for abuse of power and obstruction of Congress.

The Democratic prosecution team in the Senate trial has alleged that Mr. Trump flagrantly tried to force Kiev to help him tarnish his possible election challenger, former vice president Joe Biden. Key to the impeachment scandal is a July 25 telephone call in which Mr. Trump pushed Zelensky to announce an investigation of Biden.

Mr. Trump is accused of withholding nearly $400 million in military aid for Ukraine in the war in the east of the country, and refusing Zelensky a White House meeting unless he opened the probe.

American financial and military aid is crucial for Kiev, and that is a reason why Ukraine was struggling not to be involved in the U.S. campaign; trying to maintain support from both American major parties.

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Speaking to reporters alongside Zelensky at a news conference after their meeting, Pompeo said the "United States understands that Ukraine is an important country." He stressed America's continuing support for Kiev — including the vital financial aid that President Trump briefly withheld — and reiterated that Washington would not back down from demands that Russia revoke its "attempts to annex" the Crimean Peninsula.

"Today I'm here with a clear message: the United States sees that the Ukrainian struggle for freedom, democracy and prosperity is a valiant one. Our commitment to support it will not waiver," Pompeo said.

Pompeo repeatedly lauded the "developing" relationship between the U.S. and Ukraine, focusing on the ally as a bulwark against Russia's malign efforts in the region and in Europe more broadly. He again flatly denied that Mr. Trump had made a Zelensky White House meeting with the U.S. leader contingent upon Ukraine announcing any investigation into Biden.

U.S. Secretary of State Mike Pompeo and Ukraine's President Volodymyr Zelensky shake hands as they address the media following their meeting in Kiev on January 31, 2020. SERGEI SUPINSKY/AFP/Getty

Mr. Trump's senior diplomat praised Zelensky's efforts to fight corruption and said they would yield even greater opportunities for the two countries to deepen their economic partnership.

Zelensky also touted deepening economic ties, saying he was, "sure 2020 will be the year we significantly increase the cooperation between U.S. and Ukraine." He noted that his government was working on a deal to purchase a number of locomotives from a U.S. company, and said he hoped steel tariffs imposed by the U.S. would be eased.

Pompeo's visit was scheduled for early January but delayed because of Middle East tensions.

Pompeo said Thursday before flying to Kiev from London that he would "talk about how we can provide continuing support to the Ukrainian people from the aggressions that Russia has undertaken over the past handful of years."

He reiterated on Friday U.S. vows to back Ukraine's efforts to root out corruption.

Before the trip Pompeo declined to comment on whether he intended to raise the Biden subject during his visit to Kiev, and during his joint news conference with Zelensky it was not clear whether they had discussed it.

"I do not want to talk about particular individuals. It is not worth it," Pompeo said before he got to Kiev.

The secretary of state came under increased scrutiny last year when it emerged that he had been one of the senior administration officials listening in on Mr. Trump's July 25 phone call with Zelensky.

Mr. Trump last year removed the ambassador to Ukraine, Marie Yovanovitch, and denounced her in the call with Zelensky.

Former career diplomats accused Pompeo, a stalwart ally of the president, of not robustly defending Yovanovitch either to the White House or in public.