Kyiv, Oct 1 (AP) Ukraine's president said Tuesday that no one explained to him why millions of dollars in US military aid to his country was delayed, shrugging off suggestions that President Donald Trump froze the funding to pressure Ukraine to investigate Democratic rival Joe Biden.

Ukrainian President Volodymyr Zelenskiy is struggling to distance himself from US politics, and to contain the damage to Ukraine and his own reputation from a July phone call between him and Trump that unleashed a congressional impeachment inquiry.

"It is impossible to put pressure on me," he told reporters Tuesday.

"Many people try to influence me," he said, but "I am the president of independent Ukraine."

Zelenskiy said that in discussions with Trump, he repeatedly stressed the importance of the US military aid to help Ukraine battle Russian-backed separatists.

In the July call, he thanked Trump for his "great support in the area of defense" and said Ukraine was ready to "cooperate for the next steps," according to a rough transcript released by the White House.

Zelenskiy didn't say Tuesday whether the issue was raised in other discussions or when they took place.

The Pentagon in June announced plans to send USD 250 million in aid to Ukraine, but its delivery was delayed.

A defence official said the Trump administration was analyzing the extent to which Ukrainian was addressing long-standing US concerns about corruption.

The funding was then released in September.

"It wasn't explained to me" why the money didn't come through earlier, Zelenskiy said.

Zelenskiy also said he has never met or spoken with Trump's lawyer Rudy Giuliani, who has been pushing for Ukraine to investigate Hunter Biden's role on the board of Ukrainian gas company Burisma.

Zelenskiy is facing a dilemma over how to handle Trump's request in the July call for Ukraine to "look into" the Bidens.

If Ukraine opens an investigation into the case, that helps Trump and the Republicans. If it doesn't, that helps the Democrats. And what Ukraine's current leadership really wants is continued US support, no matter who wins next year's US elections.

A former Ukrainian security chief argued Tuesday that the best way to show that Ukraine is serious about fighting endemic, crippling corruption is to open new investigations into Burisma.

"The whole world is talking about Ukraine and the whole world wants to know what happened" at Burisma, Valentyn Nalyvaichenko told The Associated Press.

Nalyvaichenko, a parliament member who twice headed Ukraine's National Security Service, or SBU, said he will initiate a parliamentary inquiry into Burisma.

He insisted he is not trying to do Trump's bidding. "We have no way to know whether any crimes were committed if we don't lead a comprehensive, transparent investigation inside Ukraine," he said.

A previous probe was closed in 2016. (AP)

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