Ukraine activates nationwide air raid alerts with Kyiv under attack. Here's the latest

This screen grab shows people taking shelter in a subway station in Kyiv, Ukraine, on June 2. @taniakovba/Twitter/Reuters

Air raid sirens rang out across Ukraine early Friday as Kyiv's mayor reported explosions in the capital.

Meanwhile, several Russian regions, including Kursk and Belgorod, are facing their own attacks, which Russian officials have blamed on Ukraine — though Kyiv denies direct involvement.

Here's what to know:

• Attack on Kyiv: The city's mayor said early Friday that "another wave of UAVs (unmanned aerial vehicles) is heading for Kyiv," adding: "The air defense is working." This follows a missile strike on the capital the day before, which killed three people including a 9-year-old girl, who had reportedly tried to enter a bomb shelter that was closed.
• Strikes inside Russia: Dozens of strikes have occurred on Russia's border region of Belgorod over the past day, allegedly carried out by Ukrainian forces, according to the region's governor. Meanwhile, the western Russian region of Kursk shot down several Ukrainian drones, the region's governor said early Friday, urging residents to remain calm.
• Russian dissident fighters: A group of anti-Putin Russian nationals claimed Thursday it is fighting inside Russian territory, which the Russian military has denied. A second similar group said it was "near the border" with Russia. Both groups are aligned with the Ukrainian defense forces — but Ukraine's deputy foreign minister told CNN Thursday the country "does not have any responsibility" over the groups who are "acting on their own."
• Russian casualties: A spokesperson for the Eastern Grouping of the Ukrainian Armed Forces claimed that about 208,000 Russian soldiers have been killed since the beginning of the war. CNN has not been able to independently confirm these numbers, and Russia's Ministry of Defense has not released updates on its casualties since last September when it said fewer than 6,000 Russian soldiers had been killed.
• NATO bids: Sweden and Ukraine's potential membership of the military alliance were a main focus at an informal meeting of NATO foreign ministers on Thursday. NATO officials hope to admit Sweden by July 11, but Turkey and Hungary have so far blocked the move. The NATO chief told CNN they cannot make Ukraine a full member in the middle of war — but will continue to provide Kyiv with support, and build a road map for Ukraine to possibly join NATO after the war.