Ukraine's government offered a lifeline to US President Donald Trump by pledging not to divulge the contents of a call he had with Ukrainian President Volodymyr Zelensky.

In a little-noticed interview last Friday, Vadym Prystaiko, Ukraine's foreign affairs minister told the Hromadske news channel that his country will not release the contents of the call, saying: "We have our secrets."

"The president has the right to speak with another president so that this conversation remains unknown to anyone," Prystaiko said.

The call between Trump and Zelensky have ignited a political firestorm in the US, with allegations that Trump used the conversations to pressure Ukraine to investigate Hunter Biden, the son of former Vice President Joe Biden.

Hunter Biden was a board member of a Ukrainian energy exploration company called Burisma Holdings for around five years.

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The government of Ukraine offered a lifeline to US President Donald Trump by pledging not to divulge the contents of a call with Ukraine's president which has prompted calls for Trump's impeachment.

In a little-noticed interview last Friday, Ukraine's Foreign Affairs Minister, Vadym Prystaiko, said that the exchange between Trump and Ukrainian president Volodymyr Zelensky would remain private.

He told the TV channel Hromadaske: "We are an independent state, we have our secrets."

Calls between Trump and Zelensky have ignited a political firestorm in the US, following allegations that Trump inappropriately pressured Ukrainian authorities to investigate Hunter Biden, the son of former Vice-President Joe Biden, who is currently Trump's main rival for the presidency in the 2020 election.

The relevant part of the interview (in Ukrainian) starts here around the 20-minute mark:

Prystaiko said that he knows what was said in the call, but would not share it. Instead, he gave a vague summary of the "long, friendly" exchange.

The minister also appeared to give Trump relief from claims that in the call he had pressured Zelensky into investigating the Ukrainian business activities of Hunter Biden, son of Democratic frontrunner Joe Biden.

Prystaiko said: "If someone thinks that pressure has been put on our president, they should determine it. I know what the conversation was about and I think there was no pressure."

Here is the full answer:

"I think this is the confrontation they are trying to get us into ... People involved in Ukrainian-American relations understand that we have always tried to appreciate the help from both [US] parties.

"This assured us that with the change of administration we would not change our priorities in relations with the USA. Indeed, the US presidents have supported us, and we appreciate the support of Congress.

"But this does not mean that they would like to help, and even could in theory help one of the parties. We are an independent state, we have our secrets.

"The president has the right to speak with another president so that this conversation remains unknown to anyone. This is the only premise that leaders still share important and often sensitive information. US investigators have every right to contact the US to obtain this information.

"If someone thinks that pressure has been put on our president, they should determine it. I know what the conversation was about and I think there was no pressure.

"Conversations are different, leaders have the right to discuss any existing issues. This conversation was long, friendly, and addressed many issues."

In the US, the furor over Trump's dealings with Zelensky has led to renewed calls for his impeachment, including from Democratic presidential candidate Elizabeth Warren and House Intelligence Committee Chairman Adam Schiff, who was previously reluctant to support impeachment.

Also on Friday, Biden called for Trump to release the transcript of the call so that "the American people can judge for themselves" what went on.

Trump himself over the weekend seemed to toy with releasing the transcript of the call, though he previously seemed reluctant to.

According to The Hill, he told reporters: "We'll make a determination about how to release it, releasing it, saying what we said..." He added that "you have to be a little bit shy about doing that."