Western Officials Warn Russia Could Use a Dirty Bomb as a Pretext

Top officials from the United States, Britain and France demanded on Monday to call out what they said was a transparent ploy by Moscow to create a pretext for escalating the war in Ukraine.

The public effort to expose the suspected Russian maneuver, which began with a joint statement issued on Sunday by the three allies, reflected a belief in Washington, London and Paris that Putin may be preparing the ground for a sharp escalation in the war.

While the officials said that there was no change in Russia's nuclear posture, and that no decision had been made to use a tactical nuclear weapon, they made clear that a move in that direction was their main concern.

Ned Price, a State Department spokesman, said that there was no reason for the US to change its nuclear posture. We wanted to send a very clear signal after hearing these troubling statements.

Russia has a history of accusing others of doing what it is contemplating, and of attempting false flag operations that could be used to justify intervention.

Sergei K. Shoigu, the Russian defense minister, claimed over the weekend that the Ukrainians were planning to blow up a dirty bomb. Moscow's top military commander repeated the allegation in a series of calls with NATO nations on Monday.

A bomb that doesn't have the power of a nuke is not a nuke. It is an effective weapon of terror and can cause a lot of damage. It can be confused with an atomic weapon in public discussion.

After more than six months, there was a flurry of phone calls between the US, NATO and Russia. What American officials said was a greater level of concern about possible nuclear use by Russia than at any point during the war was reflected in the sudden frequencies of the calls.

The lessons of the Cuban Missile Crisis have been studied and debated by President Biden's aides. They worry that Mr. Putin may use his nuclear arsenal to try to break the alliance with the West.

The rare joint statement by the top diplomats in the United States, France and Britain had echoes of the move before the invasion of Ukraine to expose intelligence about Russia's upcoming moves. Some of those actions did not come to fruition, but Mr. Putin was not deterred from the invasion.

The three governments confirmed that their defense ministers had spoken with Mr. Shoigu, and they rejected Russia's false allegations about a dirty bomb.

The world would see any attempt to use this allegation as a pretext to escalate.

A carefully worded statement was issued by the White House press secretary.

She rejected Russia's false allegations that Ukraine was preparing to use a dirty bomb. She said that they were concerned about the false allegation being used as a pretext for further escalate. We reject these accusations. We have not seen a reason to change our own.

The accusations were made public after two conversations between the Defense Secretary and his Russian counterpart.

The foreign minister of Ukraine invited the International Atomic Energy Agency to come into the country to verify that the country is not building dirty bombs. The director general of the I.A.E.A., who is in Washington this week, was one of the people he talked to.

The United States and its allies are reminded that there are limits to Moscow's tolerance of their support for Kyiv when Mr. Putin and other Russian officials issue Nuclear Threats.

The White House decided not to use nuclear weapons during the war because they wanted to make sure the war did not get out of hand. As a result, the United States has not delivered weapons that could reach deep into Russia, even as it has stepped up its supply of arms that have had a devastating impact on the Russian army fighting inUkraine.

The phone calls and official statements over the weekend showed a growing worry. The fears were explained by Mr. Putin's actions.

In September, officials noted that Mr. Putin had various steps to take, short of using a nuclear weapon, to escalate the conflict with Ukraine. Mr. Putin has the ability to mobilize his population or launch a large-scale attack on Ukrainian infrastructure.

Less than a month later, Mr. Putin has begun attacks on the Ukrainian power grid. His army is in a state of disrepair. The missile strikes on the electric grid are meant to break the will of the Ukrainian people by plunging the country into darkness as winter approaches.

According to some officials, Mr. Putin may want to see how the moves play out before taking more steps to intensify the war.

The use of a nuclear weapon could undermine Mr. Putin.

The U.S. began to warn about Russian false flag operations before the war began. The plot by Russia to hire crisis actors to create a false pretext for invasion was uncovered by the US after Russia said that Ukraine was planning to use a chemical weapon.

Pentagon officials were on edge Monday after three phone calls in four days between the defense department's top civilian official and top uniformed officer. Mr. Austin and Mr. Shoigu spoke for the first time in five months on Friday.

Three officials said the conversation was meant to clarify why Mr. Putin raised the possibility of a nuclear attack on Ukraine.

The Defense Department was surprised when Mr. Shoigu called at 7:30 a.m. the next day. He accused Ukraine of preparing to use a dirty bomb.

Senior defense and military officials were concerned that Moscow might be using the false flag as a distraction after the United States denied the allegation.

Senior Pentagon officials were worried about Russia's next step up the ladder. A senior U.S. official said there were troubling developments with Russia's nuclear arsenal. The official asked for anonymity and refused to give any information.

There was no indication at the Pentagon that Mr. Putin had decided to use unconventional weapons.

Russian tactical nuclear weapons were not moved by American officials. Because the weapons are small, it is not certain if they will see them or hear them.

Gen. Mark A. Milley, the chairman of the Joint Chiefs of Staff, spoke with his Russian counterpart on Monday.

The military leaders agreed to keep the lines of communication open after discussing several security related issues.

Edward Wong made a contribution to the report.