Western officials warn that Russia could use a dirty bomb as a pretext

Yet the use of a nuclear weapon could most likely undermine Mr. Putin at home.

Even before the war, US officials began to warn of various Russian false flag operations that Moscow hoped to use to create a pretext for invasion. Russia, for example, said Ukraine planned to use a chemical weapon, then US intelligence uncovered a plot by Russia to hire crisis actors to create a false pretense for invasion.

Pentagon officials were on edge Monday after three phone calls in four days between the top civilian Defense Department official and the senior uniformed officer. On Friday, Mr. Austin initiated a phone call with Mr. Shoigu, his Russian counterpart, the first time the two had spoken since May.

The conversation was intended to delineate red lines that could potentially prompt Russia to launch a nuclear attack on Ukraine and clarify for the Biden administration why Mr Putin raised the prospect of a nuclear strike in Ukraine, three said. responsible.

Defense Ministry officials were surprised when two days later Mr Shoigu requested another call, at 7:30 a.m. Sunday, in which he accused Ukraine of preparing to use a dirty bomb, two officials said .

The allegation, which the United States has called unsubstantiated, has spooked senior defense and military officials, who have expressed concern that Moscow may be using the false flag as a distraction, masking another more disturbing development.

That possibility has only heightened concerns among already nervous senior Pentagon officials about Russia’s possible next step on the escalation ladder. A senior US official has said there are disturbing new developments regarding Russia’s nuclear arsenal. The official requested anonymity and declined to provide details, given the sensitivity of the issue.

During a briefing at the Pentagon on Monday, a senior US military officer said there was no indication that Mr Putin had made the decision to use unconventional weapons – nuclear, chemical or biological weapons – but no gave no details.