The White House on Monday opted for caution in reacting to FBI Director James Comey's bombshell decision to announce further investigation of Hillary Clinton's email days before the 2016 presidential election.

Spokesman Josh Earnest said he would "neither defend nor criticize" Comey, who has been blasted by Democrats since Friday.

Earnest described him as a "man of integrity" but also pointed to norms that "limit public discussion of facts that are collected in the context" of ongoing investigations.

"The president believes that it's important for those norms and traditions and guidelines to be followed," the spokesman said.