PUTIN is preparing a "huge, vicious and unrelenting" revenge assault on Ukraine, US insiders have warned.

Officials said the Kremlin 's full-scale retaliation for last week's stunning Operation Spiderweb on four key Russian airbases hasn't yet materialized - but it is coming very soon.

The revenge strike will be "asymmetrical" and likely to feature a mix of drones and missiles aimed at symbolic Ukrainian targets - not just military assets, one US official told Reuters.

Another said the operation could begin within days.

A senior Western diplomat added: "It will be huge, vicious and unrelenting.

"But the Ukrainians are brave people."

On Friday, Russia unleashed a fierce missile and drone barrage on Kyiv , killing at least six and injuring over 80, but American officials say th

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