Russia is regrouping its forces for a renewed offensive on the Ukrainian capital Kyiv, according to Ukrainian military officials, as it seeks to cut off the northern cities of Chernihiv and Sumy.

Russian forces also continued to tighten their grip around Mariupol, the port on the Sea of Azov in south-eastern Ukraine that has been subjected to fierce Russian artillery shelling for more than two weeks.

Ukrainian president Volodymyr Zelensky called for comprehensive peace talks with Moscow, warning it would take Russia several generations to recover from its losses in the war.

“The time has come to meet. The time has come to talk,” Zelensky said in a video address to the nation. “It is time to restore territorial integrity and justice for Ukraine. Otherwise, Russia’s losses will be so great that it will take you several generations to recover.”

With Russia’s war in Ukraine in its fourth week, its offensive appears to have stalled on several fronts, slowed by logistical challenges, tactical missteps and intense Ukrainian resistance.

Though it has made some headway in the south, where it captured the port city of Kherson early on in the war, its advance has been halted on the approaches to Mykolaiv, a city on the Bug estuary that is a major shipbuilding centre and one of Ukraine’s key transport hubs.

Russia has been forced to “change its operational approach and is now pursuing a strategy of attrition”, according to the UK Ministry of Defence.

“This is likely to involve the indiscriminate use of firepower, resulting in increased civilian casualties, destruction of Ukrainian infrastructure and intensify the humanitarian crisis,” the MoD said.

You are seeing a snapshot of an interactive graphic. This is most likely due to being offline or JavaScript being disabled in your browser.

Russia’s defence ministry said on Saturday it had used its Kinzhal hypersonic missile to hit a target in Ukraine for the first time, claiming it struck a munitions storage facility in the west of the country on Friday. Hypersonic weapons can travel faster than five times the speed of sound.

“The Kinzhal aircraft missile system with hypersonic ballistic missiles destroyed a large underground storage facility for missiles and aircraft ammunition of Ukrainian troops in Deliatyn in the Ivano-Frankivsk region,” ministry spokesman Igor Konashenkov said.

An update from the Ukrainian general staff said Russian forces were trying to cut off the cities of Chernhiv in the north and Sumy and Kharkiv in the north-east.

The Russians were also “trying to regroup their combat units” near Kyiv in preparation for a renewed offensive on the capital, and were preparing to attack the northeastern towns of Trostyanets and Okhtyrka.

But the general staff said Russia had “failed” in its main objectives, which included encircling Kyiv and “establishing control over the left-bank part of Ukraine”, a reference to the eastern half of the country.

More than 3mn people have fled Ukraine since Russia’s invasion began, triggering Europe’s biggest refugee crisis since the second world war. António Guterres, UN secretary-general, said the war was “disrupting supply chains and causing the prices of fuel, food and transport to skyrocket”.

“We must do everything possible to avert a hurricane of hunger and a meltdown of the global food system,” he said.

Australia imposed a ban on exports of alumina and aluminium ores to Russia on Sunday, adding to wide-ranging sanctions imposed by the US and its allies on Moscow following the invasion. “Russia relies on Australia for nearly 20 percent of its alumina needs,” the Australian government said, referring to the material that is the starting point in aluminium production.

The measures would limit Russia’s capacity to produce aluminium, a critical export, the government added.

One of the main objectives of Russia’s offensive is Mariupol, which is encircled and has endured a relentless bombardment by Russian troops. Local officials say fighting has reached the city centre and heavy shelling has kept humanitarian aid from getting in.

Thousands of people in Mariupol — which had a pre-war population of 460,000 — have been forced to live in shelters, deprived of electricity, heat and mobile services and with food and water running out.

Russia’s air force bombed Mariupol’s main municipal theatre, which had been used as a shelter by the city’s civilian population, last week. Authorities said more than 130 people had been rescued from the rubble but hundreds were unaccounted for and could still be in the building.

Capturing Mariupol would give the Russians control of the whole northern coast of the Sea of Azov, cutting Ukraine off from a crucial conduit to the Black Sea and enabling Moscow to form a land corridor to Crimea, the peninsula it illegally annexed from Ukraine in 2014.

The Ukrainian general staff said on Friday evening that Russian forces had “partially succeeded in the Donetsk theatre, temporarily depriving Ukraine of access to the Sea of Azov”.

Additional reporting by Felicia Schwartz in Sofia