Putin is so angry about Ukraine's resistance to his invasion that he might launch a more aggressive attack, Western officials warn

• Putin is growing furious over Ukrainian resistance to his invasion, US officials told NBC News.
• As a result, US officials believe Putin may escalate the situation, CNN and The Daily Beast reported.

US officials believe President Vladimir Putin is so angry with the apparent blunders that Russian troops have made in Ukraine that he may launch a more aggressive attack that would devastate the country, multiple reports say.

Since invading Ukraine last week, Russian troops have attempted to seize Kyiv, but have been met with strident resistant from Ukrainian forces.

As a result, Putin is confused, frustrated, and directing bursts of anger at people in his inner circle, NBC News reported, citing intelligence from US officials.

"The main concern is the information he's getting and how isolated he is. The isolation is a really big concern," a Western diplomat told NBC News. "We don't believe he has a realistic understanding of what's going on."

US officials also told reporters on Monday that they fear Putin will escalate his invasion given the lack of success on the ground.

"They have been slowed and they have been frustrated by their lack of progress on Kyiv, and one of the things that could result is a reevaluation of their tactics and the potential for them to be more aggressive and more overt in both the size and the scale of their targeting of Kyiv," a senior defense official told reporters on Monday, according to CNN.

Another Western official told Insider on Monday evening: "There are ... some risks that come as a consequence of Russia's lack of progress."

"I fear the way in which Russia is frustrated in achieving its aims on the ground is leading to the use of more indiscriminate fires and as a consequence we're going to see an increase in civilian casualties."

US officials also warned the country's lawmakers in a classified briefing on Monday that Russia could put Kyiv under siege and that the situation would deteriorate quickly, CNN reported.

"We're certainly mindful that the frustrations could lead to a more aggressive approach by the Russians," a US official told reporters Monday, The Daily Beast reported.

"One of the things that could result is a reevaluation of their tactics and the potential for them to be more aggressive and more overt in both the size and scale of their targeting of Kyiv."

Putin's behavior in recent weeks has been extreme, but the US has no intelligence proving that he is mentally unstable, four officials told NBC News.

However, his behavior has shocked former US officials.

"He was always hard, cold, disciplined, almost machine-like," former US intelligence chief General James Clapper told Insider's Mattathias Schwartz.

"Now his anger — fury — show. His meandering, incoherent rants are illogical and scary. He has no one who can push back and disagree with him."

Michael McFaul, a former US ambassador to Russia, told NBC's "Meet the Press" on Sunday that Putin was becoming "increasingly unhinged."

Following the invasion of Ukraine, the US, UK, the EU, and other nations imposed sanctions on Russian entities and individuals, and barred Russia from the SWIFT global financial system.

Putin called the sanctions "illegitimate" and on Sunday responded by ordering Russia's nuclear deterrent onto a "special regime."

However, British and American officials believe the move is a scare tactic, and to distract from the situation in Ukraine.