WASHINGTON: The United States believes that Russian President Vladimir Putin’s threatened retaliation against Ukraine over its drone attack last weekend has not happened yet in earnest and is likely to be a significant, multi-pronged strike, US officials told Reuters.

The timing of the full Russian response was unclear, with one source saying it was expected within days. A second US official said the retaliation was likely to include different kinds of air capabilities, including missiles and drones.

The officials spoke on condition of anonymity. They did not detail Russia’s expected targets nor elaborate on intelligence matters. The first official said Moscow’s attack would be “asymmetrical,” meaning that its approach and targeting would not mirror Ukraine’s strike last weekend against Russian warplanes.

• Putin's retaliation for Ukraine drone strike has yet to fully unfold, US officials say

• Strikes expected to including missiles, drones, US officials say