President Donald Trump on Wednesday stepped up his pressure over Apple's refusal to unlock iPhones for authorities in criminal cases.

"Apple has to help us. And I'm very strong on it," Trump told "CNBC Squawk Box" co-host Joe Kernen from the World Economic Forum in Davos, Switzerland. "They have the keys to so many criminals and criminal minds, and we can do things."

Apple CEO Tim Cook has been credited with being able to work with the president and his administration in a way other Silicon Valley companies have stumbled. In November, Cook toured Apple's Austin campus with Trump.

Trump told CNBC he's helped Apple a lot, including waivers from tariffs put on Chinese-made imports in the trade war between Washington and Beijing.

"I've given them waivers, because it's a great company, but it made a big difference," Trump said.

Last week, Trump slammed Apple for declining the government's request to unlock password-protected iPhones used by the shooter who killed three people in December at the Pensacola Naval Air Station before being fatally shot.

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In a statement, Apple said it provided gigabytes of information to law enforcement related to the Pensacola case but that it would not build a "backdoor" or specialized software to give law enforcement elevated access.

Trump told CNBC on Wednesday: "They could have given us that information. It would have been very helpful."

The president said he's not concerned about his relationship with Cook or Apple because the stakes are so high.

"You're dealing with drug lords and you're dealing with terrorists, and if you're dealing with murderers, I don't care," Trump said.