Russian news agency Sputnik claimed the detained person was identified as Ukrainian intelligence agent Ignat Kuzin.

FSB said he planted an explosive device that killed Russian Lt. Gen. Yaroslav Moskalik.

"The Federal Security Service of the Russian Federation has detained Ukrainian intelligence agent Kuzin Ignat (born 1983), a permanent Ukrainian resident, who planted an explosive device in a Volkswagen Golf car in Balashikha, the Moscow Region. The subsequent detonation killed Lieutenant General Yaroslav Moskalik (born 1966), the deputy head of the Main Operational Directorate of the General Staff of the Russian armed forces," read a statement issued by FSB.

The suspect acquired the vehicle and installed a homemade explosive device using components retrieved from a cache previously set up by Ukrainian intelligence agents in the Moscow Region, the FSB said, adding that the explosive device was remotely detonated from Ukraine as Moskalik was exiting an apartment building.

Ukraine did not comment on the explosion so far.

Russia Attack

The blast occurred a day after Russia launched a major attack on several Ukrainian cities, including Kyiv.

The latest Russian strikes reportedly damaged 12 buildings in the capital, causing widespread damage to homes, businesses and key services, while phones have been heard ringing from the rubble.

Other Ukrainian cities targeted included Zhytomyr - due west of Kyiv – and the northeastern cities of Sumy -  where a daytime missile strike killed at least 34 people on 13 April - and Kharkiv - where the authorities reported 24 drone and missile strikes in total.

“The casualty count is expected to rise as emergency teams continue search-and-rescue operations,” said the UN aid coordination office, OCHA.

The development follows Ukrainian President Volodymyr Zelensky’s reported decision on Wednesday to reject a US-led proposal to seek a peace deal with Russia that would have involved ceding territory lost during the war. In theory, this would include the eastern Ukrainian regions of Donetsk, Luhansk, Kherson and Zaporizhzhia, in addition to Crimea, which Russia annexed illegally in 2014.

“Last night’s large-scale attack by the armed forces of the Russian Federation on residential areas in Kyiv and surrounding regions is yet another appalling violation of international humanitarian law,” said the UN’s top aid official in Ukraine, Matthias Schmale.

Children and a pregnant woman were among the more than 70 people injured by Wednesday night’s reported missile and drone strikes. “This senseless use of force must stop… Civilians must never be targets”, said Schmale, UN Humanitarian Coordinator for Ukraine.