Expedited talks are under way among Kyiv and its allies about Ukraine's requests for long-range missiles that it says are needed to prevent Russia from destroying Ukrainian cities, a top aide to President Volodymyr Zelenskiy said on Saturday.

Ukraine has won promises of Western battle tanks and is seeking fighter jets to push back against Russian and pro-Moscow forces, which are slowly advancing along part of the front line.

"To drastically reduce the Russian army's key weapon - the artillery they use today on the front lines - we need missiles that will destroy their depots," presidential adviser Mykhailo Podolyak told Ukraine's Freedom television network. He said on the Russian-occupied Crimean Peninsula there were more than 100 artillery warehouses.

"Therefore, firstly, negotiations are already under way. Secondly, negotiations are proceeding at an accelerated pace," he said without giving details.

Zelenskiy, speaking separately, said Ukraine wanted to preempt Russian attacks on Ukrainian urban areas and civilians.

"Ukraine needs long-range missiles ... to deprive the occupier of the opportunity to place its missile launchers somewhere far from the front line and destroy Ukrainian cities," he said in an evening video address.

Zelenskiy said Ukraine needed the U.S.-made ATACMS missile, which has a range of 185 miles (297km). Washington has so far declined to provide the weapon.

Earlier in the day, the Ukrainian air force denied a newspaper report that it intended to get 24 fighter jets from allies, saying talks were continuing, Ukraine's Babel online outlet said.

Spain's El Pais newspaper, citing Ukrainian air force spokesperson Yuri Ihnat, said Ukraine initially wanted two squadrons of 12 planes each, preferably Lockheed Martin F-16 jets.

But in a statement to Babel, Ihnat said his comments to a media briefing on Friday had been misinterpreted.

"Ukraine is only at the stage of negotiations regarding aircraft. Aircraft models and their number are currently being determined," he said.

Ihnat told the Friday briefing that F-16s might be the best option for a multi-role fighter to replace the country's current fleet of ageing Soviet-era warplanes.

He also told Ukrainian national television that allied nations did not like public speculation about jets, Interfax Ukraine news agency said.

Deputy White House national security adviser Jon Finer on Thursday said United States would be discussing the idea of supplying jets "very carefully" with Kyiv and its allies.

Germany's defence minister this week ruled out the idea of sending jets to Ukraine.