Both Jens Stoltenberg and US Secretary of State Mike Pompeo have blamed Russia for the Cold War treaty’s collapse.
Nato and the US accuse Russia of violating the pact by deploying a new type of missile, which Russia denies.
The Intermediate-Range Nuclear Force banned missiles with ranges between 500 and 5,500km (310-3,400 miles).
The INF treaty was signed by US President Ronald Reagan and Soviet leader Mikhail Gorbachev in 1987 but its collapse more than 30 years later has raised fears of a news arms race.
Why has it ended?
Last year the Americans said they had evidence that the new Russian cruise missiles fall within the range banned by the treaty.
Accusations about the 9M729 missiles – known to Nato as SSC-8 – were then put to Washington’s Nato allies, which all backed the US claim.
In February, President Donald Trump set the 2 August deadline for the US to withdraw from the pact if Russia didn’t come into compliance.