It's been more than three weeks since Russia began its invasion of Ukraine. Russian forces are continuing their attacks on major cities across Ukraine including Mariupol in the southeast.

Russia's defense ministry said on Friday that pro-Moscow forces are tightening their encirclement of the city and fighting in its center with the support of the Russian military. However, the information has not been confirmed by Ukrainian officials.

Rescuers scrambled to pull survivors from the rubble of this bombed theater, where Ukrainian officials say hundreds of people had been sheltering. So far, 130 survivors have reportedly been rescued. Up to 100 explosions a day have been forcing more and more people from their homes.

The mayor of the western city of Lviv says missiles hit facilities near the airport on Friday. And Russian forces are believed to be preparing a push to take control of Ukraine's largest port city of Odesa.

A senior US defense official says the Russians are also trying to improve their ability to attack Kyiv from afar. The Pentagon official says the Russians have moved artillery units from the rear to join their advancing elements.

The official also says there are signs that Russian morale is flagging with troops facing shortages of fuel and other supplies.

Meanwhile, negotiators from both sides continue to talk via video link. Ukraine is demanding an immediate ceasefire and the withdrawal of Russian forces.

Both parties are believed to be discussing a framework to ensure Ukraine's security without the country joining NATO.

Russian presidential spokesperson Dmitry Peskov said on Thursday that the Russian negotiators are ready to work around the clock but that Kyiv lacks zeal.

Russian President Vladimir Putin's close aide, Security Council Secretary Nikolai Patrushev, reportedly urged US officials to exert influence on Kyiv in order to achieve speedy progress in negotiations.