Special counsel Jack Smith issued a subpoena to the Arizona secretary of state's office in May as part of the ongoing criminal probe related to efforts to overturn the 2020 election, CNN has confirmed.

Adrian Fontes' office has complied with the subpoena, which was received through outside counsel, a spokesperson for the secretary of state said Thursday.

The subpoena, first reported earlier this week by the Arizona Republic, adds to what's known about the special counsel's probe as investigators have recently zeroed in on the efforts to put forward alternate slates of electors in seven states Donald Trump lost, including Arizona. Trump and his allies also waged legal battles claiming election fraud in the state.

The news comes as a former top Republican official in Arizona, who rejected pressure from Trump and his allies following the former president's 2020 election defeat, told CNN Wednesday night that he has spoken with the FBI as part of the same ongoing criminal investigation.

Former Arizona House Speaker Rusty Bowers revealed the interview with investigators lasted four hours and took place a few months ago.

"I am hesitant to talk about any subpoenas, et cetera. But I have been interviewed by the FBI," Bowers told CNN's Kaitlan Collins, when asked whether he had been subpoenaed.

In recent weeks, federal investigators have focused on Trump's efforts, as well as those of his top lawyers as they organized fake electors to submit votes to Congress on his behalf and as they sought to sway then-Vice President Mike Pence into blocking the election result.

CNN previously reported investigators secured evidence and testimony from fake electors in Nevada, Georgia's secretary of state and various election offices in battleground states -- indicating the breadth of Smith's work to date.