Ukrainian President Volodymyr Zelenskiy says his country has developed a weapon that has hit a target 700km away in an apparent reference to a strike on an airport in western Russia.
Zelenskiy said on his Telegram channel the weapon was produced by Ukraine’s Ministry of Strategic Industries but gave no other details.
On Wednesday, a four-hour wave of drones that officials in Moscow blamed on Ukraine hit an airport near Russia’s border with Estonia and Latvia, damaging four Il-76 military transport planes, according to local reports.
The airport is in Russia's Pskov region, about 700km north of the Ukrainian border.
In all, six Russian regions were targeted in the barrage amid the 18-month war.
The Associated Press was unable to determine whether the drones were launched from Ukraine or inside Russia.
Ukranian officials normally neither claim nor deny responsibility for attacks on Russian soil although they sometimes refer obliquely to them.
Zelenskiy’s remark was the clearest hint that Ukraine was behind the strike.
The attack forced the closure of Pskov airport although it reopened on Thursday, according to Russian transport officials.
Another drone intercepted overnight near Moscow resulted in flight delays at several airports around the Russian capital, officials said on Thursday.
No injuries were reported.
Russian news agency Interfax reported, meanwhile, that security services killed two people and detained five members of a Ukrainian sabotage group in the Bryansk border region on Wednesday.
Ukrainian Foreign Minister Dmytro Kuleba on Thursday criticised critics of his country's counteroffensive strategy and the speed of the troops' advance into Russian-held territory.
Kuleba said critics are "spitting into the face" of the Ukrainian soldier "who sacrifices his life every day, moving forward, and liberating 1km of Ukrainian soil after another."
"I would recommend all critics to shut up," he added, before inviting them to "come to Ukraine, and try to liberate one centimetre squared by themselves."
In Moscow on Thursday, the Russian and Turkish foreign ministers discussed renewing a deal that would allow Ukraine to export grain from its Black Sea ports.
Russian Foreign Minister Sergei Lavrov demanded guarantees from Ukraine's allies that Russia would also be allowed to export grain and fertiliser without obstruction.
In return, Russia would be prepared to return to the grain deal that it pulled out of in mid-July.
A resumption of Ukrainian exports by sea was important to ensure world food supplies, Turkish Foreign Minister Hakan Fidan said.
This would also ensure greater stability and peace in the region, he added.
Fidan referred to proposals from United Nations Secretary-General Antonio Guterres pledging to take Russian interests into account.
Lavrov responded that Guterres' proposals were mere promises and not firm guarantees.
The sanctions imposed by the US and European countries were the reason that Russia could not export its grain and fertiliser, he said.
The European Union and other supporters of Ukraine have repeatedly insisted that the sanctions on Russia do not affect its grain exports.
In mid-July Russia lifted its guarantee of safe passage for grain shipments from Ukrainian ports.
Before that Ukraine had been able to export about 33 million tonnes of grain and other agricultural produce by sea since last year.
Overland routes are considerably more expensive and subject to capacity and other restrictions.
Lavrov said that Turkey could purchase one million tonnes of Russian grain at a discounted price.
The ministers' meeting is intended to prepare the ground for a meeting between Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan.