KYIV: Russian air strikes killed 35 people at a military base outside Ukraine's western city of Lviv, in an attack that brings the conflict dangerously close to the Polish border, reports AFP.
Another nine people were also killed in a strike on the southern city of Mykolaiv, the regional governor said, while the capital Kyiv braced for possible encirclement by Russian forces.
"The Russian invaders cannot conquer us. They do not have such strength. They do not have such spirit. They are holding only on violence. Only on terror," he said.
For the first two weeks following its February 24 invasion, Russia's forces had focused on eastern and southern areas of Ukraine, notably the strategic and heavily besieged port of Mariupol.
In recent days they moved to the centre, striking the city of Dnipro, and now the west, edging close to the frontier with EU and NATO member Poland.
Overnight, missiles struck a military training ground in Yavoriv near Lviv, about 20 kilometres (12 miles) from the Polish border, regional governor Maxim Kozitsky said.
He said 35 people were killed and 134 injured in the attack on the base, which was a training centre for Ukrainian forces with foreign instructors, including from the United States and Canada.
The city of around 500,000 has been under attack by Russian troops for days and an AFP reporter said a cancer treatment hospital and an eye clinic there came under fire Saturday.
Meanwhile, efforts continue to get help to the strategic southern port city of Mariupol, which aid agencies say is facing a humanitarian catastrophe.
A convoy of aid headed for Mariupol was blocked at a Russian checkpoint, but hoped to arrive on Sunday, Ukraine's Deputy Prime Minister Iryna Vereshchuk said.
Ukraine says more than 1,500 civilians have died in a near two-week siege, which has left the city without water or heat, and running out of food.
Attempts to evacuate hundreds of thousands of people have repeatedly failed.
"Mariupol is still surrounded... Since they cannot bring down the Ukrainian army, they target the population," a French military source said.
A top Russian officer described the situation in stark language.
"Unfortunately, the humanitarian situation in Ukraine is continuing to deteriorate rapidly, and in some cities, it has reached catastrophic proportions," said the head of the Russian National Defence Control Centre, Mikhail Mizintsev.
The Russians have advanced far enough to raise fears of Kyiv becoming encircled imminently.
Other cities have already fallen or been surrounded, with civilians targeted in what the United Nations warned could amount to war crimes.
In his video address, Zelensky appealed for more aid.
"I keep reiterating to our allies and friends abroad; they have to keep doing more for our country, for Ukrainians and Ukraine. Because it is not only for Ukraine, but it is for all of Europe," he said.
He said "about 1,300" Ukrainian soldiers had been killed since February 24, giving his country's first official toll.
He claimed Russia had lost about 12,000 troops while Moscow, for its part, has only given a toll of 498 dead, released on March 2.
At least 579 civilians have been killed, according to a tally Saturday by the United Nations, which stressed that its figures were probably much lower than reality.
The UN estimates that almost 2.6 million people have fled Ukraine since the invasion, most of them to Poland, in Europe's worst refugee crisis since World War II.
In Kyiv, only the roads to the south remain open and the city is preparing to mount a "relentless defence", according to the Ukrainian presidency.
Kyiv mayor Vitali Klitschko said the capital was stockpiling food and medicine, while civilians are being brought in on buses from bombed-out suburbs. Britain's ministry of defence estimated that Russian forces were about 25 kilometres from Kyiv on Saturday and that a column north of the city had dispersed, reinforcing the indication of an attempt to encircle it.
However, the Russians are encountering resistance from the Ukrainian army to both the east and west of the capital, according to AFP journalists on the spot.
Meanwhile, a US journalist was shot dead and another wounded on Sunday in Irpin, a frontline northwest suburb of Kyiv, medics and witnesses told AFP.
Danylo Shapovalov, a surgeon volunteering for the Ukrainian territorial defence, said one of the Americans died instantly and he had treated the other.
AFP reporters in Irpin saw the body of the victim. A third victim, a Ukrainian who had been in the same car as the Americans, was also wounded.
Ukrainian officials were quick to blame Russian forces for the shooting but the exact circumstances were unclear. AFP reporters heard small arms and artillery fire in the area.
"The car was shot at. There were two journalists and one of ours (a Ukrainian)," Shapovalov told AFP.
"Our guy and the journalist are wounded, I provided them first aid, the other one received a wound in the neck, he died immediately."
Papers found on the American reporter's body identified him as 50-year-old video documentary shooter Brent Renaud, of New York.