A third Russian airfield was set ablaze by a drone strike, a day after Ukraine demonstrated an apparent new ability to penetrate hundreds of kilometres into Russia with attacks on two air bases.

Officials in the Russian city of Kursk, about 90km north of the Ukraine border, released pictures of black smoke above an airfield after the latest strike on Tuesday. The governor said an oil storage tank had gone up in flames but there were no casualties.

On Monday, Russia said it had been hit hundreds of kilometres from Ukraine by what it said were Soviet-era drones - at Engels air base, home to Russia's strategic bomber fleet, and in Ryazan, a few hours' drive from Moscow.

Ukraine did not directly claim responsibility for the strikes but nonetheless celebrated them.

Late on Tuesday, sirens sounded on the territory of the airfield in Engels, Russian state-run news agencies reported, citing Yevgeny Shpolsky, first deputy of the Engels district administration.

In Washington, US Secretary of State Antony Blinken repeated his country's determination to provide Ukraine with the equipment it needs to defend itself while saying it had neither encouraged nor enabled the Ukrainians to strike inside Russia.

Russia's defence ministry said three service members were killed in the attack at Ryazan. Although the attacks struck military targets, it characterised them as terrorism and said the aim was to disable its long-range aircraft.

Ukraine never publicly acknowledges responsibility for attacks inside Russia. Asked about the strikes, Defence Minister Oleskiy Reznikov repeated a longstanding joke blaming carelessness with cigarettes. "Very often Russians smoke in places where it's forbidden to smoke," he said.

The damage to the warplanes also caused grumbling among Russian military bloggers, whose social media posts can provide a window into the mood in Russia during the course of the war.

'Leverage and control'

At least 20 oil tankers queuing off Turkey face more delays to cross from Russia's Black Sea ports to the Mediterranean as operators race to adhere to new Turkish insurance rules added ahead of a G7 price cap on Russian oil, industry sources said.

The disruption in tanker traffic was not the result of the price cap on Russian oil agreed upon by a coalition of G7 countries and Australia, an official with the group said.

The price cap of US$60 a barrel was imposed on Monday at a level above the current price for Urals crude from Russia, the world's second-largest oil exporter.

G7 countries and Australia would be busy in the coming weeks determining two more price cap levels on Russian refined oil products slated to be in place by Feb 5, a US Treasury official told Reuters.

"I think the point is that we have all the leverage and all the control now that we've been able to set the ceiling at US$60," the official said. "Any adjustments will be in the interest of the G7 and will be in the interest of Ukraine, it will be in the interest of the world economy and will not be in the interest of Russia."

Zelenskiy with troops

Meanwhile, on the battlefields of eastern, northeastern and southern Ukraine, Russian forces kept up their shelling of towns and villages, the Ukrainian military said late on Tuesday.

Six people were killed as Donetsk came under rocket and artillery fire, the Russian-installed city mayor, Alexander Kulemzin, reported in his Telegram channel.

"Look what they have done," said a resident named Irina, gesturing towards the apartment building where her flat had been destroyed. "There are people living over there. People! Where do you fire? Go in the fields and fight each other over there, not here. How many people are dying already."

Dmytro Zhyvytsky, the governor of Sumy region on the Russian border, said several people were wounded when Russian forces fired 226 shells on seven communities during the day.

War crimes investigators are looking into the deaths of hundreds of civilians since the beginning of the near 10-month conflict. Russia denies targeting civilians during what it calls a special operation to rid Ukraine of dangerous nationalists.

Ukrainian President Volodymyr Zelenskiy visited troops close to the front lines in eastern Ukraine on Tuesday.

Addressing military personnel later in the presidential palace in Kyiv, Zelenskiy said he had spent the day with troops in Donbas, theatre of the heaviest battles, and in Kharkiv region, where Ukrainians have retaken swaths of territory from Russian forces.

"Thousands of Ukrainians have given their lives so that the day might come when not a single occupying soldier will remain in our land and when all our people will be free," Zelenskiy, clad in his trademark khaki green, told the gathering.

- Reuters