Ukraine’s president has said that no one explained to him why millions of dollars in US military aid to his country was delayed, shrugging off suggestions that US 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 Mr Trump that unleashed a congressional impeachment inquiry.

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

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

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

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

Mr Zelenskiy did not say on Tuesday whether the issue was raised in other discussions or when they took place.

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

A defence official said the Trump administration was analysing 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 did not come through earlier, Mr Zelenskiy said.

TrumpPresident Donald Trump meets with Ukrainian President Volodymyr Zelenskiy during the United Nations General Assembly last week (Evan Vucci/AP)

Mr Zelenskiy also said he has never met or spoken with Mr 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.

Mr Zelenskiy is facing a dilemma over how to handle Mr Trump’s request in the July call for Ukraine to “look into” the Bidens.

If Ukraine opens an investigation into the case, that helps Mr Trump and the Republicans.

If it does not, 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 on 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.

Mr Nalyvaichenko, a parliament member who twice headed Ukraine’s National Security Service (SBU) said he will initiate a parliamentary inquiry into Burisma.

He insisted he is not trying to do Mr Trump’s bidding.

“We have no way to know whether any crimes were committed if we do not lead a comprehensive, transparent investigation inside Ukraine,” he said.

A previous probe was closed in 2016.