In an interview with ITV, Trump warned that the Chilcot Inquiry into the 2003 invasion, which will finally be published on July 6, will not look good for the former Labour PM.
“[President George W.] Bush got us into it, that’s a terrible, terrible thing that happened,” he said.
“Tony Blair made a mistake. You can’t just go in haphazardly. You folks got involved in that mess just as we did and now look at it.”
Trump said UK leaders should put the needs of their own country before that of America, and would get more respect if they stood up to US presidents.
“I’m surprised somebody would see the Bush relationship as being that important.”
Trump also criticized Lord Alan Sugar, who hosts the UK version of the Apprentice, but is critical of the Republican’s campaign.
“He’s small time. Don’t forget that Sugar works for me. Every time he makes money from that show he pays me.”
Trump also denied claims he saw Princess Diana as the “ultimate trophy wife” or had any interest in wooing her despite once claiming he could have “nailed” her.
His comments come a day after he said he is unlikely to have a “very good relationship” with Prime Minister David Cameron.
He also called newly elected London Mayor Sadiq Khan “ignorant” and in need of an IQ test because he criticized Trump’s proposal to ban Muslims from entering the US.
In response, Khan has invited Trump to London to meet his wife and teenage daughters.
The capital’s first Muslim mayor is standing by his attack on “ignorant” Trump, but has now offered the Republican an olive branch.
“I invite Donald Trump to come to London. Meet my wife and daughters. Meet my friends and neighbors. Meet Londoners who are British: they’re Londoners, they’re Muslim,” he told ITV.
“You know the great thing about London? Muslims, Christians, Jews, Hindus, Sikhs, Buddhists… we don’t just tolerate each other, we respect, we celebrate, we embrace.
“And my concern is this. Are you inadvertently making our countries less safe by giving the impression there is a clash of civilizations?
“Are you doing the job of Daesh and the extremists for them by saying the West hates Islam? I am the West!” he said, using an Arabic pejorative term for Islamic State (IS, formerly ISIS/ISIL).