Former prime minister John Howard has refused to back US Republican presidential contender Donald Trump, saying his behaviour is “not compatible with democracy”.

Howard, who took Australia into Afghanistan and the Iraq war alongside the US while he was PM, said Trump’s refusal to accept the result of the 2020 US election meant he did not want him to return to the White House in November.

“In normal circumstances, I would unhesitatingly favour a Republican victory, but there are reasons that prevent me doing that on this occasion,” Howard told the Nine Network on Thursday.

“I think his refusal to accept the result of the last election and various attempts to overturn that result not compatible with democracy.”

But Howard, who was prime minister from 1996 to 2007 and is now a senior Liberal figure, stopped short of backing Trump’s Democratic rival, Kamala Harris.

“When you play the democratic game, you’ve got to accept the democratic result … The choice the American people must make is a difficult choice – I’m glad I don’t have a vote there, because I think it would be very hard,” he said.

“I’m not impressed with Kamala Harris. I don’t think she’s got a very good idea of how to run the American economy.

“I worry that she might lead an administration that will spend far too much, and some of that expenditure will be irresponsible … she leads a party that, generally speaking, favours far too much government intervention for my liking.”

The latest comments follow similar remarks at a Liberal Party fundraiser earlier in September. At that event, Howard – who famously lost his own seat when Kevin Rudd’s Labour won the 2007 election – turned to a cricket analogy to make his point about Trump’s 2020 loss.

“He didn’t leave the field when the umpire’s finger went up,” Howard, a long-time cricket fan, said.

The 85-year-old also compared the American system with Australia’s – and found it wanting. Political events had shown up major deficiencies in the US, he said.

“Everything we’re witnessing in America tells us is that their political system is far inferior to ours,” he said.

“In a parliamentary system, Donald Trump would never have got to the leadership of the Republicans, and I don’t think Kamala Harris would ever have got to the leadership of the Democrats.

“We wouldn’t have gone through the agony the Democrats went through regarding Joe Biden.

“They have a different system. And my take, my very strong view, is that a parliamentary system is much better than a presidential system.”

Quizzed on Howard’s comments, outgoing Albanese government minister Bill Shorten refused to endorse them.

Shorten told ABC radio on Friday that Howard was “entitled his opinion”. The comments were “a pretty interesting development [and] I think his party should listen carefully to what he says”, he said.

But Shorten said as a serving member of the federal government, he would “work with whoever America produces [via] their electoral processes”.

“Get back to me on the 1st of February … or sometime in February on that one,” said Shorten.

He will take up a job as vice-chancellor at the University of Canberra when he quits politics in February.

“But I do think that the January 6 riots were shocking. I do think it’s a matter of record that more could have been done by the outgoing president,” Shorten said.

“But you know, John Howard has got the freedom of not being in politics, and I have the privilege of serving in a cabinet.”