These are the key developments from day 1,391 of Russia’s war on Ukraine. Here is where things stand on Tuesday, December 16: A Russian drone attack killed a 62-year-old Ukrainian man as he was riding a bicycle in the Velyka Pysarivka community of Ukraine’s Sumy region, Governor Oleh Hryhorov said in a post on the Telegram messaging app.

Sergey Ryabkov told ABC News Moscow cannot compromise on key territories.

The U.S. has agreed to provide unspecified security guarantees to Ukraine as part of a peace deal to end Russia's nearly four-year war, and more talks are likely this weekend, U.S. officials said Monday following the latest discussions with Ukrainian President Volodymyr Zelenskyy in Berlin.

The NATO issue is what the Kremlin describes as a "root cause" of its war in Ukraine.

Donald Trump's envoy will meet the Ukrainian president and European leaders in Berlin to discuss the latest peace plan.

The Russian submarine was allegedly carrying Kalibr cruise missiles, which Russia has used in devastating strikes on critical infrastructure and military targets across Ukraine. The SBU said the submarine was “put out of action” as a result of the blast. The FT could not independently verify the claim.

Ukraine has used long-range drones to attack Russian oil platforms as it expands its strikes on the country's energy sector.

The European Union is set to lock up Russia’s assets in Europe until Russia ends its war on Ukraine and compensates for the damage.