Former U.S. Vice President Joe Biden addresses the Human Rights Campaign (HRC) dinner in Washington, U.S., September 15, 2018. REUTERS/Yuri Gripas

WASHINGTON (Reuters) - U.S. federal investigators are trying to track down a suspicious package they believe was addressed to former Vice President Joe Biden, a federal official said on Wednesday.

Former President Barack Obama was among the targets of at least five suspected package bombs sent to high-profile Democrats and CNN in what New York officials branded an act of terrorism.