Former Republican US presidential candidate Ted Cruz. REUTERS/Pearl Gabel Ted Cruz questioned the integrity of FBI Director James Comey on Tuesday after Comey said the bureau would not recommend charges be filed against Hillary Clinton in the agency's probe of her use of a private email server as secretary of state.

"While I have tremendous respect for the dedicated men and women of the FBI, I have serious concerns about the integrity of Director Comey's decision, and how it threatens the rule of law," Cruz said in a statement.

The Texas senator added: "Director Comey has rewritten a clearly worded federal criminal statute. In so doing, he has come dangerously close to saying that grossly negligent handling of classified information should not result in serious consequences for high-level officials. In a nation where the rule of law is supposed to matter, this is troubling."

Cruz, who ran for president in 2016, called for "full access" to "all the information that the FBI used to come to today's dubious decision."

The comments came after House Speaker Paul Ryan said the decision not to recommend charges against Clinton "defies explanation."

"Based upon the director's own statement, it appears damage is being done to the rule of law," Ryan said.

Presumptive Republican presidential nominee Donald Trump has repeatedly said he believes the "system is rigged" and suggested President Barack Obama may have influenced the decision.

Comey acknowledged at a Tuesday news conference that it was illegal for officials to "mishandle classified information either intentionally or in a grossly negligent way." He characterized Clinton's handling of such intelligence as "extremely careless" but nevertheless said the bureau would not recommend that the Department of Justice file charges.