WASHINGTON, Feb 7 - Some Russian defense officials have worried that a large-scale invasion of Ukraine would be costlier and more difficult than Russian President Vladimir Putin realizes, CNN reported Monday citing four people familiar with the intelligence.

Three of the sources said those officials include intelligence and military operatives.

There is no evidence that these officials are opposed to the overall plan, or would revolt against Putin's orders, two of the sources said. Another source familiar with the US intelligence noted that Russia has a professional military that would be expected to effectively carry out Putin's orders.