KYIV, Ukraine: Concerns that the Ukraine war could escalate into a wider conflict grew on Tuesday as Kyiv accused Moscow of trying to create unrest in a Russian-backed separatist region of Moldova.

The United Nations and United States warned of rising tensions in the Transnistria region of Moldova, as UN chief Antonio Guterres met with Russian President Vladimir Putin in Moscow and pleaded for peace.

Russian forces have been in Transnistria for decades after the predominantly Russian-speaking region seceded from the former Soviet republic.

Blasts this week targeting the state security ministry, a radio tower and military unit came after a Russian commander claimed Russian speakers in Moldova were being oppressed.

The claim triggered alarm that Moldova could be Russia's next target as Moscow used the same "false flag" argument after launching its bloody invasion of Ukraine on February 24.

"Russia wants to destabilise the Transnistrian region," Mykhaylo Podolyak, a Ukraine presidential aide wrote on Twitter.

"If Ukraine falls, tomorrow Russian troops will be at Chisinau's gates," he said, referring to Moldova's capital.

Guterres "is following with concern reports of new security incidents in the Transnistrian region of Moldova," a UN spokesman said.

The United States echoed similar concerns, stopping short of backing Kyiv's contention that Russia was responsible.

"We fully support Moldova's territorial integrity and sovereignty," State Department spokesman Ned Price told reporters.

Arms flow into Ukraine

Ukraine's President Volodymyr Zelensky has been lobbying for heavier firepower to push back the Russian advance now focused on the eastern region of Donbas.

Western allies are wary of being drawn into an outright war with Russia, but Washington pledged Tuesday at a summit to move "heaven and earth" to enable Ukraine to emerge victorious.

"Ukraine clearly believes that it can win and so does everyone here," US Defense Secretary Lloyd Austin told 40 allies gathered at the Ramstein Air Base in Germany.

With arms flowing into Ukraine, Germany announced Tuesday it would send anti-aircraft tanks -- a sharp U-turn dropping its much-criticized cautious stance.

"I can say one thing: the Ukrainian army will have something to fight with," Dmytro Kuleba, Ukraine's foreign minister, said in a briefing on Facebook.

"We have entered a completely new phase.... But this is just the beginning. Much more will come to us."

The Ukrainian defence ministry reported in its latest update that fighting was raging across the east with shelling of Kharkiv city and Russian troops launching an offensive on the town of Barvinkove near Izium.

'I made a wish'

"I miss my kickboxing training and dance classes," nine-year-old Alina, who has slept in an underground car park in Kharkiv through a barrage of Russian rockets since the war began over two months ago, told AFP.

"Victory would make me very happy. The war won't end straight away, but it will in a few weeks, I made a wish."

At the entrance to Barvinkove, not far from the Russian lines, six Ukrainian soldiers were ready at any moment to dive into their trench, which they dig every day with a shovel.

"Otherwise, we're dead," said Vasyl, 51, who serves with his 22-year-old son Denys.

Ukraine officials said there was fighting all along frontlines in the Donetsk region, and that resistance in the Azovstal factory in the besieged port city of Mariupol was still holding out.

Fierce Ukrainian fighting in recent weeks has beaten back Russian troops from around the capital Kyiv and from the Chernobyl nuclear zone.

But Zelensky said Tuesday that Russian troops' conduct at Chernobyl showed that "no one in the world can feel safe."

Russia treated the toxic site "like a normal battleground, territory where they didn't even try to care about nuclear safety," he said during a press conference with UN atomic watchdog chief Rafael Grossi.

Ukraine's best-known singer Sviatoslav Vakarchuk made a morale-boosting visit to the eastern front, where a military press officer admitted the situation was difficult.

"It's far from rosy," Iryna Rybakova, of the 93rd brigade, told AFP. "Of course, we were prepared for this war, especially the professional army, but for those who've been recruited, it's more complicated."

Guterres, at his talks with Putin, called for Moscow and Kyiv to work together with the UN to set up aid and evacuation corridors to help civilians escape.

After "very frank talks" with Foreign Minister Sergei Lavrov, Guterres said that "Russia's invasion of Ukraine is a violation of its territorial integrity and against the Charter of the United Nations."

The UN chief's spokesman said Putin had agreed in principle to the United Nations and the International Committee of the Red Cross being involved in evacuating civilians from Mariupol.

Despite the bloodshed, Putin -- who shocked the world by sending troops into Ukraine -- told Guterres that he believed peace negotiations could succeed.

"We still hope that we will be able to reach agreements on the diplomatic track," Putin said.

Sitting across from the UN chief at a long table at the Kremlin, Putin said efforts at talks had been derailed by claims of atrocities committed by Russian forces.

Civilians flee

Russia said it had carried out high-precision missile strikes against 32 Ukrainian military targets including four ammunition depots on Tuesday. It also launched airstrikes against 33 targets and 100 artillery and rocket strikes.

In the south, two Russian missiles struck the industrial city of Zaporizhzhia, which has welcomed many civilians fleeing Mariupol, regional authorities said.

Russian forces are expected to soon advance on the city, giving them the potential to seize Ukraine's largest nuclear power plant.

Strikes on Tuesday killed at least nine civilians in the south and east, Ukrainian officials said.

The UN's refugee agency said it now expects more than eight million Ukrainians to eventually flee their country, with nearly 5.3 million already out, and that $1.85 billion would be needed to host them in neighbouring countries, mainly Poland.