Microsoft co-founder and philanthropist Bill Gates said Sunday he is disappointed in President Trump for slashing the U.S. budget for foreign aid.

"In terms of the first budget that he came out with, no, that was a disappointment to us," Gates said on "Fox News Sunday." "It was taking the medical research budget; culled [the National Institutes of Health], bringing that down fairly dramatically; taking the aid programs, including the ongoing HIV commitments. Definitely, I was disappointed."

Gates is now in the process of lobbying Congress to reinstate the money, particularly global health funding, which was cut by about a quarter to $6.5 billion for 2018. This is important because the U.S. is not giving "percentage-wise" as much as its European counterparts like the U.K., Germany, Sweden and Norway, Gates said.

Gates added he and his colleagues at the Gates Foundation have predicted the provision of vaccines would suffer most under the decision as inoculation is an expensive process.

"We took HIV and we modeled what even just a 10 percent cut would mean and it's an additional 5 million deaths between now and 2030," Gates said. "If that's not fully funded until we get a breakthrough like a vaccine, then the death rate is going to go back up and reach new records."

Gates said he has met twice with Trump, once in November and again in March, to discuss innovation in global health, energy, even education, but he had not yet given up on emphasizing the importance of international development to the administration.

"What we have given is phenomenal," he said, before saying foreign aid stabilizes countries and regions. "People like Secretary [of Defense Jim] Mattis have said, if you cut the development budget, you're going to have to spend more on bullets, because you're simply not there averting these problems of instability."