This was reported by TASS with reference to Antonov's comment.
The ambassador appreciated the Politico article, in which, citing sources, it is said that the US authorities are considering scenarios for equipping strategic carriers with additional nuclear charges if the START Treaty is not extended.
“At the same time, we state that it was precisely the inaction of the [American] administration that, in fact, drove the situation with the START extension into time trouble,” Antonov said.
He recalled that the Russian side had offered to extend the agreement over the past years.
Antonov also said that "the possibility of preserving the treaty is being hedged by the American negotiators with conditions that are obviously unacceptable for Russia, which do not take into account our concerns in the sphere of strategic stability."
Earlier, the US President's Special Representative for Arms Control Marshall Billingsley spoke about the extension of the START Treaty.