Russian troops are pressing their offensive across Ukraine, pounding populated areas with artillery and airstrikes and deploying siege tactics honed in Syria and Chechnya — where front line cities were reduced to rubble.

The port city of Mariupol was again a focus of intense shelling Saturday, with Russian forces striking an area around a mosque that was sheltering more than 80 people, including children. There was no immediate word of casualties from the shelling surrounding the mosque.

Bombardment intensified as Russian units fanned out to prepare their assault on Ukraine’s capital, Kyiv, a major political and strategic prize for Russian President Vladimir Putin.

Ukrainian President Volodymyr Zelenskyy said Russia would need to carpet-bomb Kyiv and kill its residents to take the city, and he encouraged his people to keep resisting.

“They will come here only if they kill us all,” Zelenskyy said. “If that is their goal, let them come.”

Now in its third week, the war has expanded to areas in western Ukraine, closer to NATO members Poland and Romania. Meanwhile residents in some besieged areas have faced so much firepower they can’t even bury the dead. The war has forced more than 2.5 million people to flee Ukraine. The Ukrainian chief prosecutor’s office says at least 79 children have been killed since the invasion began.

Here are some key things to know about the war:

WHAT’S HAPPENING IN BESIEGED MARIUPOL?

The Ukrainian government said a mosque in the city’s center was shelled, but an unverified Instagram post by a man claiming to be the mosque association’s president said the mosque itself wasn’t hit, but a bomb fell about 750 yards (700 meters) away.

The Ukrainian Embassy in Turkey said 86 Turkish nationals, including 34 children, were among those who had sought safety in the mosque.

Ukrainian authorities have warned of a humanitarian catastrophe in Mariupol, besieged by Russian forces and where Ukraine’s military said Russian forces have captured the city’s eastern outskirts.

Repeated attempts to bring in food and evacuate civilians have been cancelled due to relentless Russian fire. Zelenskyy said Russians are bombing the city 24 hours a day, while Moscow accuses the Ukrainians of violating cease-fires.

Mariupol’s mayor says the 12-day assault has killed over 1,500 people.

Doctors Without Borders said some residents are dying for lack of medication, with the city without drinking water or medicine for over a week now. The aid group says people are resorting to boiling water from the ground or extracted from heating pipes.

WHAT HAPPENED TO THE MAYOR OF MELITOPOL?

Zelenskyy has accused Russia of kidnapping the mayor of the occupied city of Melitopol, west of Mariupol and near Crimea, calling it “a new stage of terror.”

Kirill Timoshenko, the deputy head of Ukraine’s presidential office, posted a video which he said shows armed men taking Mayor Ivan Fedorov across a square. Russian forces captured Melitopol, with a population of 150,000, on Feb. 26. The video could not be immediately independently confirmed. Another video subsequently published online showed hundreds of Melitopol residents marching in a central square, demanding the mayor’s release.

The prosecutor’s office of the Luhansk People’s Republic, a Moscow-backed rebel region in eastern Ukraine, accused Fedorov on its website of “terrorist activities.”

WHAT’S HAPPENING ON THE GROUND IN UKRAINE?

In the northeast, Russian forces were blockading Kharkiv, Ukraine’s second-largest city, even as efforts have been made to create new humanitarian corridors around it and other urban centers.

Ukraine’s emergency services reported that the bodies of five people were pulled from an apartment building that was struck by shelling in Kharkiv, including two women, a man and two children.

In multiple areas around Kyiv, heavy artillery fire sent residents scurrying for shelter as air raid sirens wailed. An ammunition depot outside the city was shelled overnight, sending billowing black smoke into the sky, according to video provided by emergency workers.

Britain’s Defense Ministry said Russian ground forces that had been north of Kyiv for most of the war had edged to within 25 kilometers (15 miles) of the city center and spread out, likely to support an attempted encirclement.

Commercial satellite images appeared to capture artillery firing on residential areas that stood between the Russians and the Ukrainian capital. The images from Maxar Technologies showed muzzle flashes and smoke from big guns, as well as impact craters and burning homes in the town of Moschun, 33 kilometers (20.5 miles) from Kyiv, the company said.

WHAT HAS THE AP DIRECTLY WITNESSED OR CONFIRMED?

An Associated Press journalist witnessed tanks firing on a 9-story apartment block in Mariupol and was among a group of medical workers who came under sniper fire on Friday. Conditions at a local hospital there were deteriorating, electricity was reserved for operating tables and the hallways were lined with people with nowhere else to go.

Anastasiya Erashova, wept and trembled as she held a sleeping child. Shelling had just killed her other child as well as her brother’s child. “No one was able to save them.”

The city of 430,000 has been without food, running water and electricity for 10 days.

In Baryshivka, a village east of Kyiv, people surveyed damage and boarded up windows after a Russian bombing reduced a restaurant and a cinema to hanging metal, dust, glass and other debris. Ivan Merzyk, a 62-year-old resident, said: “Putin created this mess, thinking he will be in charge here. Ukrainians are a free nation. We are not going away from here and we don’t want to see any Russian here.”

ARE THERE TALKS TO STOP THE FIGHTING IN UKRAINE?

The office of French President Emmanuel Macron said he was on a three-way call Saturday with German Chancellor Olaf Scholz and Russian President Vladimir Putin. Macron’s office said the call was “very frank and also difficult.”

The Kremlin said Putin laid out his demands for ending the war, including Ukraine’s demilitarization. Moscow has also demanded that Ukraine drop its bid to join NATO, adopt a neutral status and acknowledge Russian sovereignty over Crimea, among other things.

Macron said Friday the European Union will continue applying pressure to Moscow and consider all options for more sanctions if Putin intensifies bombing. Among some of the sanctions, the U.S. and its allies are downgrading Russia’s trade status, which would allow for higher tariffs to be imposed on Russian imports.

(AP)