Speaking on the sidelines of a NATO foreign ministers' meeting in Prague, Stoltenberg said the alliance had heard such warnings many times before and self-defence was not escalation, Reuters reported.
"This is nothing new. It has ... been the case for a long time that every time NATO allies are providing support to Ukraine, President Putin is trying to threaten us to not do that," he told reporters.
Putin on Tuesday warned NATO members against allowing Ukraine to fire their weapons into Russia and raised once again the risk of nuclear war after several allies lifted restrictions imposed on the use of weapons donated to Kyiv.
In a marked policy shift, US President Joe Biden approved Ukraine using US weapons to strike targets inside Russia that were attacking the Ukrainian city of Kharkiv, US Secretary of State Antony Blinken confirmed in Prague.
He said Washington's move was a result of a US strategy of adjusting and adapting to the battleground, indicating that Moscow's attacks on Kharkiv have necessitated this.
SD/PR