The top US intelligence official outlined the most imminent security threats facing the United States in 2016 for the Senate Armed Services Committee, touching on disruptions in cyberspace, Islamic State's attack capabilities and the continued nuclear ambitions of North Korea and Iran.

Director of National Intelligence James Clapper told senators that Islamic State remains the "pre-eminent terrorist threat" in the world.

"They've attempted or conducted scores of attacks outside of Syria and Iraq in the past 15 months. ISIL's estimated strength worldwide exceeds that of al-Qaeda. ISIL leaders are determined to strike the US homeland beyond inspiring homegrown violent extremist attacks. Although the US is a much harder target than Europe by ISIL external operations remain a critical factor in our threat assessment for 2016," he said, using an acronym for Islamic State.

US Defense Intelligence Agency Director, Lieutenant General Vincent Stewart, spoke on some issues including North Korea's nuclear capability.

Stewart said that recent developments, including their sixth space launch over the weekend, "highlight Pyongyang's commitment to diversifying its missile force and nuclear delivery options."