The top US army general on Sunday warned Kyiv and the West to remain vigilant over how Russia might react to the latest setbacks on the battlefield in Ukraine.

"The war is not going too well for Russia right now," said US Army General Mark Milley, chairman of the Joint Chiefs of Staff, "So it's incumbent upon all of us to maintain high states of readiness, alert."

Milley cautioned that the war was in a new phase in which Ukrainian forces have seized the strategic initiative, recapturing large swaths of territory in the northeast and south of Ukraine in recent days.

"Because of that, we have to very closely watch what Russia's reactions to that will be," he added.

Milley was speaking to reporters in Warsaw after visiting a Polish military base.

The US and its NATO allies are aiding Ukraine from a distance in its counteroffensive against Russia's aggression.

While Russian President Vladimir Putin has brushed off the recent rout of his forces by Kyiv's military, he warned Friday that Moscow would respond more forcefully if its troops were put under further pressure.

Here's a roundup of some of the other key developments regarding Russia's invasion of Ukraine on September 18.

Zelenskyy: Ukraine's forces readying for next phase of counteroffensive

Ukrainian President Volodymyr Zelenskyy has vowed that there would be no letup in the counteroffensive against Russia's military aggression, despite Russian shells targeting civilian areas over the weekend.

In his nightly video address, Zelenskyy said: "Maybe now it seems to some of you that after a series of victories we have a certain lull."

"But this is not a lull. This is preparation for the next phase... Because Ukraine must be free — all of it."

Russian fire killed four medics attempting to evacuate a psychiatric hospital in the Kharkiv region on Saturday. Overnight shelling also hit a hospital in Mykolaiv, a significant Black Sea port. Also, five people died over the past day in Russian attacks in the eastern Donetsk region.

Biden warns Putin against tactical nuclear attack

US President Joe Biden gas warned his Russian counterpart Vladimir Putin against using chemical or tactical nuclear weapons in the wake of serious losses in Moscow's war in Ukraine.

"Don't. Don't. Don't," he told the US TV show "60 Minutes" in an interview broadcast Sunday.

"You would change the face of war unlike anything since World War II," Biden said.

Asked what the US response would be, Biden said such an action would be "consequential."

"They will become more of a pariah in the world than they have ever been," the president said. "And depending on the extent of what they do will determine what response would occur."

Tactical nuclear weapons can be used over short distances and are generally smaller in power, although modern tactical warheads are still several times more powerful than the ones used by the US during World War II in Hiroshima and Nagasaki.

UK: Russia increased targeting civilian infrastructure

The British Defense Ministry said in its regular intelligence update that Russia had increased targeting civilian infrastructure in the last week, "even where it probably perceives no immediate military effect."

The report noted the strikes on a dam on the Inhulets River at Kryvyi Rih in southern Ukraine, one of the country's largest urban areas. The strike caused flooding and subsequent damage that Ukrainian authorities are still repairing.  

"As it faces setbacks on the front lines, Russia has likely extended the locations it is prepared to strike in an attempt to directly undermine the morale of the Ukrainian people and government," the ministry added. 

Zelenskyy accuses Russia of Nazi practices 

Ukrainian President Volodymyr Zelenskyy said investigators had found evidence of "10 torture chambers" in recaptured towns in the northeastern Kharkiv region. 

"Torture was a widespread practice in the occupied territories. That's what the Nazis did — this is what [the Russians] do," Zelenskyy said in a video address late on Saturday.

"They will answer in the same way —  both on the battlefield and in courtrooms," he vowed. 

Earlier this week, Zelenskyy said more than 400 bodies were discovered in a mass grave in the town of Izium in Kharkiv after Ukrainian forces recaptured it as part of a counteroffensive operation. 

Australia won't ban Russian tourists 

Australian Defense Minister Richard Marles said the country was not considering a ban on Russian tourist visas as part of its sanctions on Moscow. 

Speaking with Australian broadcaster ABC, Marles said Canberra's sanctions on Moscow were aimed at the Russian government, "not the Russian people themselves."

Australia has sanctioned hundreds of Russian individuals and institutions linked to Russia's banking sector and sovereign debt since the beginning of the war in Ukraine.

Canberra has also banned some exports to Russia and supplied military and humanitarian supplies to Ukraine. 

"We will be looking at how we can provide that ongoing support," Marles said, adding that Australia was "one of the largest non-NATO military support of Ukraine."

mm, fb/dj (dpa, Reuters)