Pentagon documents leak a risk to US national security, officials say

A leak of classified US Defence Department documents is a "very serious" risk to national security, the Pentagon has said.

The documents appear to include sensitive information regarding the war in Ukraine, as well as on China and US allies.

Officials say the files are in a format similar to documents issued to senior leaders.

An investigation has been opened to determine the source of the leak.

The documents - some of which officials say may have been altered - first appeared on online platforms such as Twitter, 4chan and...