Russian air defenses on Tuesday foiled a Ukrainian drone attack on Moscow that prompted authorities to briefly close one of the city’s international airports, officials said, as a Western analysis said Russia has managed to slow Kyiv’s recently launched counteroffensive.

The attack, which follows recent similar raids on the Russian capital, was the first known assault on the Russian capital since an abortive mutiny launched 11 days ago by mercenary chief Yevgeny Prigozhin that saw his Wagner troops approach Moscow in the biggest – though short-lived – challenge to Russian President Vladimir Putin in more than two decades of his rule.

Ukrainian authorities, which generally avoid comments on attacks inside Russia’s proper territory, didn’t claim responsibility for the raid.

The Russian Defense Ministry said four of five drones were downed by air defenses on Moscow’s outskirts and the fifth was jammed by electronic warfare means and forced down.

Moscow Mayor Sergei Sobyanin said that there were no casualties or damage.

The drone attack prompted authorities to temporarily restrict flights at Moscow’s Vnukovo airport and divert flights to two other Moscow main airports. Vnukovo is about 9 miles southwest of Moscow.  The restrictions were lifted after the drone attack was repelled.

Foreign ministry spokeswoman Maria Zakharova said on Telegram that, “An attempt by the Kyiv regime to attack a zone where civil infrastructure is located, including an airport that receives international flights, is a new terrorist act,” according to Agence France-Presse.

In May, two daring drone attacks jolted the Russian capital in what appeared to be Kyiv’s deepest strikes into Russia.  

Tuesday’s raid came as Ukrainian forces continued probing Russian defenses in the south and east of their country in the initial stages of a counteroffensive.

Oleksiy Danilov, the secretary of Ukraine’s Security and Defense Council, charged that the military was currently focusing on destroying Russian equipment and personnel and claimed that the last few days of fighting have been particularly “fruitful.”

He provided no evidence for his claim and it wasn;t possible to independently verify it.

The Ukrainians are up against minefields, anti-tank ditches and other obstacles, as well as layered defensive lines reportedly up to 12 miles deep in some places as they attempt to dislodge Russian occupiers.

The U.K. Defense Ministry said Tuesday the Kremlin’s forces have “refined (their) tactics aimed at slowing Ukrainian armored counteroffensive operations in southern Ukraine.”

Moscow has placed emphasis on using anti-tank mines to slow the onslaught, the assessment said, leaving the attackers at the mercy of Russian drones, helicopters and artillery.

“Although Russia has achieved some success with this approach in the early stages of Ukraine’s counteroffensive, its forces continue to suffer from key weaknesses, especially overstretched units and a shortage of artillery munitions,” the assessment said.

Western analysts say the counteroffensive, even if it prospers, won’t end the war that started with Russia’s full-scale invasion in February 2022.

Russia, meanwhile, has continued its missile and drone barrage deep behind the front line.  

Oleksandr Lysenko, mayor of the city of Sumy in northeastern Ukraine, said three people were killed and 21 others were injured in a Russian drone strike Monday that damaged two apartment buildings.

Ukrainian President Volodymyr Zelenskyy said the attack also damaged the regional headquarters of the Security Service of Ukraine, the country’s main intelligence agency. He argued that the country needs more air defense systems to help fend off Russian raids.