US President Donald Trump (r) and Apple CEO Tim Cook speak to the press during a tour of the Flextronics computer manufacturing facility where Apple's Mac Pros are assembled in Austin, Texas, on November 20, 2019.

In a tweet, President Donald Trump slammed Apple over whether it should unlock password-protected iPhones used by the shooting suspect at a Navy base in Pensacola, Florida in December.

"We are helping Apple all of the time on TRADE and so many other issues, and yet they refuse to unlock phones used by killers, drug dealers and other violent criminal elements. They will have to step up to the plate and help our great Country, NOW! MAKE AMERICA GREAT AGAIN," Trump tweeted.

On Monday, Attorney General William Barr claimed that Apple had not provided "substantive assistance" in unlocking the alleged shooter's two iPhones.

In a statement late Monday, Apple responded that that it had 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.

"We reject the characterization that Apple has not provided substantive assistance in the Pensacola investigation. Our responses to their many requests since the attack have been timely, thorough and are ongoing," Apple said.

The tweet, sent from an iPhone, also suggested that Apple should work with the FBI because Trump helps "Apple all of the time on TRADE."