Barack Obama has chided Donald Trump as “wacky” and “uninformed” after the Republican candidate said Russia’s President Putin was a better leader.
Speaking in Laos, Mr Obama said that every time Mr Trump spoke it became clearer that the Republican contender was not qualified to be president.
In a televised forum on Wednesday, Mr Trump had praised Mr Putin’s “great control” and 82% approval rating.
Mr Trump and rival Hillary Clinton had taken questions from military veterans.
Mr Obama said: “I don’t think the guy’s qualified to be president of the United States and every time he speaks, that opinion is confirmed.”
The president pointed to the diplomatic work he had faced at both the Asean summit in Laos and the earlier G20 meeting in China.
He said: “I can tell you from the interactions I have had over the last eight or nine days with foreign leaders that this is serious business.
“You actually have to know what you are talking about and you actually have to have done your homework. When you speak, it should actually reflect thought-out-policy you can implement.”
Mrs Clinton, meanwhile, pilloried Mr Trump for having suggested US military leaders had been “reduced to rubble”, accusing him of having “trash-talked American generals”.
In a rare press conference, she said on Thursday morning: “That’s how he talks about distinguished men and women who’ve spent their lives serving our country, sacrificing for us.”
Mr Trump had told the forum in New York that the Russian president had “been a leader far more than our president has been”.