KYIV—Ukraine said Wednesday it reclaimed more territory from Russia in the south and welcomed the delivery of Western air defenses Kyiv said would herald a "new era" after mass strikes by Moscow.

Russia for two days pummelled Ukraine with missiles, damaging energy facilities nationwide, in attacks that President Vladimir Putin said were retaliation for a deadly explosion at the Crimea bridge.

Moscow's FSB security service said Wednesday it detained eight suspects over the blast that ripped through the road and rail bridge connecting Crimea to Russia.

But it also claimed to have foiled two more attacks that Ukrainian special services allegedly planned to carry out on Russian territory.

NATO chief Jens Stoltenberg said Wednesday after Russia's missile barrage that Ukraine's Western backers were looking to provide Kyiv with more air defenses to protect against Russia's "indiscriminate" attacks across the country.

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"The top priority will be more air defense for Ukraine," Stoltenberg said at the start of a meeting by Ukraine's allies on arms supplies to Kyiv.

United States Defense Secretary Lloyd Austin said after the meeting "the systems will be provided, as fast as we can physically get them there".

Putin has vowed a "severe" response to any further attack on Russia and what Moscow considers to be its territory, including the Crimea peninsula that it annexed from Ukraine in 2014.

Despite warnings from the Kremlin, Kyiv has vowed to retake the peninsula, as well as four regions in Ukraine's east and south that Moscow says are now part of Russia.

Kyiv said Wednesday that it had retaken five more settlements in the southern region of Kherson -- one of the four territories Moscow said it annexed in late September -- in the latest setback for Russia's campaign.

- Putin 'miscalculated' -

The Russian military meanwhile said it had fended off Ukrainian attacks in the eastern Donetsk, Lugansk and Kharkiv regions.

And Russian strikes on the frontline town of Avdiivka killed at least eight people at a market, the Ukraine-appointed chief of the region said.

The Ukrainian army announced its counter-offensive in the south in late August.

After regaining almost full control of the northeastern region of Kharkiv, Ukrainian forces recently claimed more gains on the eastern and southern fronts.

Faced with mounting setbacks since September, the Russian president announced the mobilization of hundreds of thousands of reservists to join the fighting in Ukraine.

With the Crimea bridge blast, Russia also lost a vital transport link for moving military equipment for its soldiers fighting in Ukraine.

US President Joe Biden said Tuesday that he believes his Russian counterpart "miscalculated" the situation in Ukraine and underestimated the ferocity of Ukrainian defiance.

"He thought he was going to be welcomed with open arms, that this was the home of Mother Russia in Kyiv," Biden told CNN in a rare televised interview.

"I think he just totally miscalculated."

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Putin is due to meet Turkish President Recep Tayyip Erdogan in Kazakhstan later this week, with a Kremlin official suggesting Ankara will formally offer to mediate talks between Russia and Ukraine.

- Mass graves discovered -

After two days of nationwide Russian strikes that especially targeted Ukraine's energy infrastructure, leaving villages and towns without power and hot water, Ukraine said it had started receiving anti-aircraft defense systems from its Western allies.

"A new era of air defense has begun in Ukraine," Defence Minister Oleksiy Reznikov said on Twitter, announcing the arrival of Germany's Iris-Ts and the upcoming delivery of NASAMS from Washington.

He said he had met with Austin and General Mark Milley and discussed the "strengthening of the combat potential of the Ukrainian army", according to a tweet.

On Tuesday, Ukraine's President Volodymyr Zelensky called on the G7 club of wealthy nations to help Kyiv create an "air shield", warning that Russia "still has room for further escalation".

On the frontline in Donetsk, Western weapons have helped boost Ukrainian morale and the abilities of Kyiv's forces.

"We definitely need more artillery," said an officer who gave his name as "Sergiy" with Ukraine's 5th Regiment on a hill overlooking Russian-held Gorlivka in Donetsk.

"When it comes to artillery, they still have an advantage so we can't return fire equally.

"We are firing more precisely now, but with fewer strikes," Sergiy said about the US-made Mk-19 automatic grenade launcher.

In two towns elsewhere in the Donetsk region, Ukrainian officials announced Tuesday the recovery of the remains of dozens of civilians found at mass burial sites.

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In Lyman, a railway hub retaken by Ukraine in early October, a forensic team dressed in protective gear was exhuming dozens of bodies, an AFP journalist saw.

More than 50 bodies of both soldiers and civilians were found, officials said.

Russian forces have been accused of numerous abuses -- torture, rape, extrajudicial executions -- in Ukraine, claims Moscow has repeatedly denied.