Ukrainian drones have the capability of striking a target up to 1,550 miles away, but Moscow has been protected, a senior Russian airforce official has said.
The comments, made by Dmitry Bogdanov, head of the radio-electronic warfare department of the Russian Aerospace Forces, suggest a wide swath of Russian territory bordering Ukraine is vulnerable to attack.
"The enemy is not standing still," Mr Bogdanov was quoted as saying by state news agency Tass.
"Now unmanned aerial vehicles can traverse an area of up to 2,500 kilometres, and many [Russian] regions are aware of this."
It comes after a Kyiv source told Reuters on Monday that a Ukrainian drone had attempted its deepest strike yet, targeting a Russian early-warning military radar system in the Orenburg region, almost 1,000 miles away.
Since the start of the year, drone attacks have also struck critical oil refining infrastructure in Russia.
Ukraine does not officially confirm or deny it is attacking refineries inside Russia, but it says such sites are legitimate targets as they aid Moscow's military effort.
A major barrage in May last year saw two drones fly towards the Kremlin complex overlooking Red Square before they were destroyed.
