Ukrainian officials will not testify in the US Congress in the impeachment inquiry into Donald Trump without an official summons because Kyiv does not want to get involved in the internal affairs of another country, Ukraine’s foreign minister has said.

“We don’t have any connection to this,” Vadym Prystaiko told reporters on the sidelines of an investment conference in Mariupol on Tuesday. “They should deal with it themselves. We won’t go there, we won’t comment.”

Ukrainian officials have previously said they hadn’t received any official requests for information from the White House or Congress in an ongoing impeachment inquiry into the president.

Democrats are investigating whether there are grounds to impeach Trump for asking Ukraine’s president, Volodymyr Zelenskiy, to publicly open an investigation into an affair involving Trump’s political rival, former vice-president Joe Biden.

Asked whether Kyiv would share information about contacts between Ukrainian and American officials, Prystaiko said: “We could tell them if they ask us.”

Trump allegedly withheld military aid and delayed a White House meeting with Zelenskiy as incentives to open an investigation into Biden and his son Hunter, according to testimony from a former top US diplomat in Ukraine, Bill Taylor.

On Tuesday, congressional impeachment investigators were expected to hear new testimony from a Ukraine expert on the national security council (NSC) who complained to government lawyers about the 25 July call between Trump and Zelenskiy.

“I did not think it was proper to demand that a foreign government investigate a US citizen, and I was worried about the implications for the US government’s support of Ukraine,” Lt Col Alexander S Vindman planned to testify.

Zelenskiy and other Ukrainian officials could shed light on demands made by Trump; the US ambassador to the EU, Gordon Sondland; and Rudy Giuliani, a personal attorney to the US president. Even before his inauguration, Zelenskiy had already consulted advisers on how to navigate pressure from Trump to investigate Biden, according to the Associated Press.

Kyiv is currently fighting a war against Russian-backed separatist forces that has left more than 14,000 dead. Democrats say that the withholding military aid for Trump to secure personal political gains is an impeachable offence.

Prystaiko downplayed the scandal, saying that it was normal for two countries to use informal channels in diplomacy and that relations between the two countries have not been negatively affected.

He also sought to distance Ukraine’s presidential administration from questions about a potential investigation into Burisma, the company where Biden’s son Hunter was a board member, saying questions should be addressed to Ukraine’s general prosecutor’s office.

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