A Red Cross convoy intended to evacuate survivors from the besieged city of Mariupol is mounting a second rescue mission after a first attempt was foiled by fierce fighting and Russian shelling.

The latest bid to reach and extract survivors comes as as Russian forces look to be regrouping for new attacks in the southeast.

Mariupol, encircled since the early days of Russia’s five-week-old invasion, has been Moscow’s main target in Ukraine’s southeastern region of Donbas.

Tens of thousands of people there are trapped with scant access to food and water.

The International Committee of the Red Cross (ICRC) sent a team on Friday to lead a convoy of about 54 Ukrainian buses and other private vehicles out of the city, but they turned back, saying conditions made it impossible to proceed.

“They will try again on Saturday to facilitate the safe passage of civilians,” the ICRC said in a statement.

Repeated attempts foiled

A previous Red Cross evacuation attempt in early March failed because the route was found to be unsafe.

Russia and Ukraine have agreed to humanitarian corridors during the war that have facilitated the evacuation of thousands of civilians.

The ICRC says its Mariupol operation has been approved by both sides, but major details were still being worked out, such as the exact timing and destination of the convoy, which would be an undetermined location in Ukraine.

In an early morning video address, Ukrainian President Volodymyr Zelensky warned that Russian troops had moved toward the Donbas region and northeast in the direction of Kharkiv, Ukraine’s second-largest city, where previous Russian strikes badly damaged urban areas.

“I hope there may still be solutions for the situation in Mariupol,” Zelenskiy said.

“The whole world has to react to this humanitarian catastrophe.”

Mr Zelensky also accused retreating Russian forces of sowing booby traps as they abandoned captured towns in the face of unrelenting Ukrainian counterattacks, claiming that corpses were trip-wired to mines.

In Chuhuiv, a city in Kharkiv province, casualties suffering shrapnel and gunshot flooded a hospital. Two women sat on neighbouring beds, limbs bandaged and pinned in metal braces.

Russian President Vladimir Putin sent troops on February 24 for what he calls a “special operation” to demilitarise Ukraine and “denazify” its leadership.

The West calls it an unprovoked war of aggression that has killed thousands, uprooted a quarter of Ukraine’s population and brought tensions between Russia and the United States to their worst point since the Cold War.

US cancels missile test

Aiming to lower nuclear tensions with Russia, the US military cancelled an intercontinental ballistic missile test that it had initially aimed only to delay, the Air Force told Reuters.

But the United States and its European allies have sent Ukraine military assistance, including an additional $US300 million ($A400 million) dollars in aid announced by the Pentagon late on Friday. The new aid includes laser-guided rocket and anti-drone systems.

Washington will also work with allies to transfer Soviet-made tanks to Ukraine to bolster its defences in Donbas, the New York Times said, citing a US official. The Pentagon declined to comment to Reuters, while the White House did not immediately respond.

At peace talks this week, Russia said Donbas, where it has backed separatists fighting Ukrainian forces since 2014, would now be the focus of its war efforts. Russian troops left behind shattered villages and their own abandoned tanks as they moved away from the capital Kyiv.

After failing to capture a single major city, Russia has painted its drawdown of forces near Kyiv as a goodwill gesture in the peace negotiations. Ukraine and its allies say Russian forces have been forced to regroup after suffering heavy losses due to determined Ukrainian resistance.

Across the border from Kharkiv in the Russian city of Belgorod, Moscow said Ukrainian helicopters struck a fuel depot on Friday, causing a huge fire. Ukraine denied responsibility for the incident, the first of its kind in the war.

Russia will strengthen its western borders so it won’t “cross anyone’s mind to attack,” Kremlin spokesman Dmitry Peskov said.

Facing unprecedented sanctions, Russia had threatened to cut off gas supplies to Europe unless buyers paid with roubles. Europe vowed to stay united against Russia’s demand, and Moscow said it would not halt supplies until new payments are due later in April.

-AAP