The U.S. Federal Bureau of Investigation reportedly said Friday it would help enforcement officials across the country to unlock mobile devices which are involved in investigations as much as “legal and policy constraints’’ allow.

The law-enforcement agency has seen surge of interest from state and local authorities after it announced that an outside party had helped it unlock an iPhone used by the San Bernardino, California, shooter. The FBI also withdrew from a 6-week long legal battle with Apple Inc., after trying to force the company to unlock the mobile phone seized in the probe of the terror attack that happened in December.

Apple had vehemently opposed the warrant, arguing that creating a backdoor into its mobile operating system could expose millions of customers to hacking or snooping.

Earlier this week, the FBI denied reports that it was assisting Arkansas authorities in unlocking an iPhone 6 connected to a double murder. However, the FBI is now testing to see if the method it used to crack the iPhone 5c will work against other types of iPhones, the Wall Street Journal reported.

The difficulty of accessing locked data in criminal probes “is a substantial state and local law-enforcement challenge that you face daily,’’ FBI reportedly said in a letter to local authorities, according to the Journal.

The letter goes on to pledge an “open dialogue” with local officials, saying: “Please know that we will continue to do everything we can to help you consistent with our legal and policy constraints.’’

“We are in this together,’’ the letter ended.