Speaking to heads of international news agencies at an economic forum in the city of Saint Petersburg, Putin said Washington showed no genuine interest in conducting talks on extending the New START treaty which caps the number of nuclear warheads well below Cold War limits.

"If no-one feels like extending the agreement -- New START -- well, we won't do it then," Putin said.

"We have said a hundred times that we are ready (to extend it)," Putin said. "There is no formal negotiating process."

The treaty was signed by US President Barack Obama and Russian counterpart Dmitry Medvedev in Prague in 2010. It expires in 2021.

Together with another agreement known as the Intermediate-Range Nuclear Forces (INF) treaty, New START is considered a centrepiece of superpower arms control.

Moscow suspended participation in the INF treaty in March after President Donald Trump's White House announced it would ditch the key agreement for alleged Russian violations of the terms.

Putin accused Washington of eroding the global arms control regime by pulling out of the bilateral Anti-Ballistic Missile Treaty in 2002 and then dropping out of the INF treaty in February.

Putin said the potential implications of letting New START treaty expire would be huge, suggesting it could fuel a nuclear arms race.

"If we don't keep this 'fiery dragon' under control, if we let it out of the bottle -- God forbid -- this could lead to global catastrophe," Putin said.

"There won't be any instruments at all limiting an arms race, for example, the deployment of weapons in space."

"This means that nuclear weapons will be hanging over every one of us all the time."

- 'Total silence' -

Putin said he was puzzled by the absence of a global discussion.

"Will anyone think about it, speak up, show some concern?" the Russian leader said. "No -- total silence."

Putin said he discussed the issue with Trump during their phone talks in early May.

"Donald told me that he is also concerned," Putin said, adding that US Secretary of State Mike Pompeo whom he hosted the same month also spoke "in a similar vein."

"If they think like this, then it is necessary to take practical steps towards joint work," the Kremlin chief said.

Putin said all nuclear powers -- both officially recognised as possessing nuclear weapons and not -- should take part in future talks.

"We have to create a broad platform for discussions and decision-making," Putin said. "That could be the light at the end of the tunnel."

Pompeo and Trump have called for the START treaty to be expanded to include China, which has already rejected the idea.

- 'Serious mistake' -

Trump's domestic rivals in the Democratic Party have also voiced concern over the lack of negotiations.

In a letter to Trump on Wednesday, senior Democrats in Congress urged him to extend New START through to the end of 2026.

"We believe that a decision to forego the benefits of New START by failing to extend the agreement would be a serious mistake for strategic stability and US security," said the letter signed by eight lawmakers including Eliot Engel, who chairs the House Foreign Affairs Committee.

At the same time, the Russian president said Moscow would not be afraid of shelving the treaty because it was developing a new generation of weapons that will "ensure Russia's security" in the long term.

"When it comes to creating hyper(sonic) weapons, we have overtaken our competitors."

Alexander Khramchikhin, an analyst with the Moscow-based Institute of Political and Military Analysis, said Putin apparently meant what he said.

"It appears that New START will not be extended," he told AFP.

Khramchikhin said he feared only a major crisis -- comparable to the Cuban Missile Crisis of 1962 -- would prompt countries to negotiate new arms control deals.

"I just don't see any other options."