Ukraine and Russia launch overnight drone attacks amid missile strike tensions

LONDON -- Ukraine's air force said that at least 73 Russian attack drones entered the country's airspace on Saturday into Sunday morning, after a week in which both sides made battlefield history with new advanced weapons systems.

Ukraine's air force said it downed 50 of the 73 Russian drones that crossed into the country. Another 19 drones were lost in flight, while four more were still flying in Ukrainian airspace as of just after 7 a.m. local time.

Russia's Defense Ministry reported downing 36 Ukrainian drones overnight Saturday and early Sunday.

The ministry said its own strikes were part of a wider campaign of attacks on "military airfields, production facilities and storage sites for drones, as well as concentrations of enemy manpower and military equipment."

Drone exchanges have been a constant element of Russia's full-scale invasion of its neighbor, with the size and regularity increasing as the war wears on. Russia also often combines its UAV barrages with missile strikes.

"This week, the air alert sounded almost every day throughout Ukraine," President Volodymyr Zelenskyy wrote on Telegram early Sunday.

"During the week, Russia used more than 800 guided aerial bombs, about 460 attack drones and more than 20 missiles of various types against Ukraine and our people," he added.

"Ukraine is not a weapons testing ground," Zelenskyy wrote. "Ukraine needs more air defense, and we are working on this with our partners. It is very important to strengthen the protection of our sky."

Tensions rose last week following Ukraine's use of ATACMS long-range missiles against military targets in Bryansk -- the first time Kyiv had used the advanced American weapon on Russian soil.

A U.S. official also confirmed to ABC News the first Ukrainian use of British Storm Shadow cruise missiles in Russia's western Kursk region, with a wounded North Korean general among the casualties.

The Kremlin response to Tuesday's ATACMS attack was furious.

Russian President Vladimir Putin signed off long-planned changes to Russia's nuclear doctrine within hours of the strike. Kremlin spokesperson Dmitry Peskov said the changes meant "the use of Western non-nuclear rockets by the Armed Forces of Ukraine against Russia can prompt a nuclear response."

Russia followed up its latest round of nuclear threats by striking with a new intermediate-range ballistic missile in the Ukrainian city of Dnipro on Thursday. Moscow warned the U.S. of the "Oreshnik" missile strike 30 minutes beforehand.

"We consider ourselves entitled to use our weapons against military objects of those countries that allow to use their own weapons against our objects," Putin said shortly after the strike. "In the event of an escalation of aggressive actions, we will respond decisively and in a mirror manner," the president added.

Zelenskyy, meanwhile, said Moscow's retaliatory strike showed that "Putin is terrified." The Russian leader, he added, "is doing whatever it takes to prevent his neighbor from breaking free of his grasp."

Yehor Cherniev -- a member of the Ukrainian parliament and the chairman of his country's delegation to the NATO Parliamentary Assembly -- told ABC News that Kyiv would not be cowed by Russian threats.

"Ukraine has every right to use the entire arsenal of available conventional weapons to the full depth of the aggressor's territory," he said, shortly after the ATACMS strike in Bryansk.

"We will continue to strike military targets on the territory of the Russian Federation until the threat to Ukraine is eliminated," Cherniev said.

ABC News' Luis Martinez contributed to this report.