(Bloomberg) -- President Vladimir Putin can be expected to brandish threats to use nuclear weapons against the West if stiff Ukrainian resistance to Russia’s invasion continues, draining conventional manpower and equipment, according to a new assessment by the Pentagon’s Defense Intelligence Agency.

“Protracted occupation of parts of Ukrainian territory threatens to sap Russian military manpower and reduce their modernized weapons arsenal, while consequent economic sanctions will probably throw Russia into prolonged economic depression and diplomatic isolation,” Lieutenant General Scott Berrier, director of the Defense Intelligence Agency, said in its new 67-page summary of worldwide threats.

The combination of Ukraine’s defiance and economic sanctions will threaten Russia’s “ability to produce modern precision-guided munitions,” Berrier said in a statement prepared for the House Armed Services Committee. 

“As this war and its consequences slowly weaken Russian conventional strength,” Berrier added, “Russia likely will increasingly rely on its nuclear deterrent to signal the West and project strength to its internal and external audiences.” 

Putin already has announced that he’s put Russia’s nuclear arsenal on a state of higher alert.

Unlike a report on global threats issued by multiple intelligence agencies last week with findings that predated the Russian invasion, the new report reflects information as of Tuesday.

A senior Pentagon official told reporters Thursday that the invasion is largely stalled, with Russia relying so far on more than 1,000 long-range missile strikes into Ukraine.

“U.S. efforts to undermine Russia’s goals in Ukraine, combined with its perception that the United States is a nation in decline, could prompt Russia to engage in more aggressive actions not only in Ukraine itself, but also more broadly in its perceived confrontation with the West,” Berrier said.

A key motivation for the invasion, he said, is Russia’s determination “to restore a sphere of influence over Ukraine and the other states of the former Soviet Union.” 

He added that “despite greater than anticipated resistance from Ukraine and relatively high losses in the initial phases of the conflict, Moscow appears determined to press forward by using more lethal capabilities until the Ukrainian government is willing to come to terms favorable to Moscow.”

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