Former CIA Director John Brennan said on Monday there was enough contact between Americans and Russian officials during the 2016 U.S. election that there was definitely grounds for an investigation into possible collusion with Moscow, and also concern about Russian efforts to recruit Americans.

"I had unresolved questions in my mind about whether or not the Russians had been successful in getting U.S. persons, involved in the campaign or not, to work on their behalf," Brennan testified to the U.S. House of Representatives Intelligence Committee.

Brennan declined to provide any indication about the identity of those people.

(Reporting by Patricia Zengerle and Doina Chiacu; Editing by Jeffrey Benkoe)