Hillary Clinton’s unsecured home server contained some closely guarded secrets, including material requiring one of the highest levels of classification, the US government has confirmed.
The revelation comes just three days before the Iowa presidential nominating caucuses in which Mrs Clinton is a candidate.
The State Department will release more emails from Mrs Clinton’s time as US secretary of state later on Friday.
But The Associated Press has learned that seven email chains are being withheld in full for containing “top secret” material.
Department officials would not describe the substance of the emails or say if Mrs Clinton had sent any herself.
Spokesman John Kirby tells the AP that no judgment on past classification was made. But the department is looking into that, too.
BREAKING: State Department declares 22 emails on Hillary Clinton's account `top secret'; won't release them.— The Associated Press (@AP) January 29, 2016