What happened. Jens Stoltenberg, the Secretary-General of NATO emphasized, if Russian occupation troops attacked supply channels NATO members use for military help transmission to Ukraine, it would be considered as an attack on Alliance in general.
The source. It is reported by CBC News.
More details. “The allies help Ukraine to protect its right for self-defendance enshrined in the UN Charter”, – Stoltenberg said. “Russia is an aggressor, Ukraine defends itself. If they attack any of NATO states or NATO territory, it will lead to the Chapter 5 application. According to this article, an attack on any of the NATO member countries is considered an attack on the entire Alliance.