Can you help me with "would've", Califjim?

UK gave Russia an ultimatum until midnight yesterday to explain about nerve-agent attack on the former Russian spy. Russia ignored the ultimatum. It's unlikely here Russian people say that president Putin would have been likely to respond to that ultimatum yesterday. It's in the video at the following link. The sentence is at two minutes and nine seconds.

Is "would've been" a third conditional sentence or past of will have? If not, how does it work in the sentence? I saw this on Fox News. Please help. Thanks.