Ukrainian president Volodymyr Zelensky has pleaded with the international community to provide more military supplies and to impose tighter sanctions on Russia as his foreign minister said he had one demand of Nato: “Weapons, weapons and weapons.”

The pleas from Kyiv come as Ukraine’s military warned that invading Russian troops were regrouping and preparing an offensive in the eastern Donbas region, aimed at seizing territory in the two administrative regions that separatists have partially occupied since a Moscow-backed uprising in 2014.

“The main efforts of the occupiers are focused on preparing for an aggressive operation in eastern Ukraine, which aims to establish complete control over the territory of the Donetsk and Luhansk regions,” the general staff of the armed forces said on Thursday after Russian troops retreated from the suburbs of Kyiv and the north of the country in recent days.

Ukrainian military authorities on Wednesday called on residents living in Donetsk and Luhansk, as well as parts of the north-eastern Kharkiv region, to leave “while they still had the chance”.

“My agenda is very simple. It only has three items on it,” Ukraine’s foreign minister, Dmytro Kuleba, said on Thursday ahead of a meeting of Nato foreign ministers in Brussels that he will attend. “It’s weapons, weapons, and weapons.”

“The more weapons we get, and the sooner they arrive in Ukraine, the more human lives will be saved,” he added.

That echoed a plea from Zelensky who said failing to provide more weapons and toughen sanctions on Russia would equate to giving Moscow “permission” to intensify its offensive.

“If there won’t be a really useful packet of sanctions against Russia, if there won’t be the really necessary supply of weapons to us, the weapons for which we have asked many times . . . this will look to Russia like permission, like permission to go farther,” he said in a late-night address. “Like permission to begin a new bloody wave in the Donbas.” 

Zelensky also called on individual Russians to demand an end to the war as it entered its seventh week.

“In demanding peace, it is better to lose something, to face down the Russian repressive machine, than to be equated with Nazis for the rest of your life,” he said.

Nato member countries have supplied Ukraine with anti-tank missiles, drones and other defensive weaponry, but have refused to supply some other classes of weapons or to impose a no-fly zone over the country, as its government has demanded, over concerns it would risk engaging Russia in a wider war.

The US this week approved $100mn in security assistance for Ukraine to buy Javelin anti-tank systems.

Kuleba, standing beside Nato secretary-general Jens Stoltenberg, said he was asking Nato for military aircraft, missiles, armoured vehicles and heavy air defence systems.

Stoltenberg said he had “urged allies to provide further support of many different types of systems” and that more weapons for Ukraine would be “one important issue at the meeting today”.

In addition to supplying Ukraine with weapons, western countries have sought to punish Russia with economic sanctions. Washington imposed its most severe sanctions on Sberbank, Russia’s biggest financial institution, and Alfa-Bank, its biggest private bank, on Wednesday, further tightening the economic pressure on Moscow, as the EU moved to target more oligarchs and ban coal imports from Russia.

Calls to bolster Ukraine’s defences and toughen sanctions on Russia have multiplied this week after evidence emerged of atrocities carried out by Russian troops before they pulled out of Kyiv’s outskirts.

Ukrainian troops, government officials and journalists found the corpses of hundreds of civilians, some with indications they had been tortured, and heard accounts of summary killings, rape and other human rights abuses from surviving residents.

Kuleba said Ukraine was still demanding a “full oil and gas embargo for Russia”.

He added that he hoped it would not take more allegations of war crimes to force the west to take additional measures.

“Frankly speaking, I hope we will never face a situation again when we . . . need atrocities like Bucha to be revealed and to impress and to shock other partners to the extent that they sit down and say OK, fine, we will introduce new sanctions,” Kuleba added.

Russia has denied the allegations and state media have accused Ukraine of faking the killings, including by employing actors.

US president Joe Biden, French president Emmanuel Macron and other leaders have called for an investigation of Russian officials responsible for what they called war crimes.

The UN General Assembly is due to vote on Thursday on whether to suspend Russia from its Human Rights Council.

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