Volodymyr Zelenskiy has accused Russian forces of seizing a humanitarian convoy near Mangush west of Mariupol. “Employees of the state emergency service and bus drivers have been taken captive. We are doing everything to set our people free and unblocked the movement of humanitarian cargo,” he said in his latest address on Telegram. He said about 100,000 people remained in Mariupol “in inhumane conditions. In a total blockade. Without food, water, medication. Under constant shelling, under constant bombing”.

Russian forces are now inside the besieged southern city, a senior US defence official said. Two “super-powerful bombs” rocked Mariupol on Tuesday even as rescue efforts were ongoing, local authorities said.

The deputy head of Kyiv’s police force has accused Russia of using white phosphorous munitions in the city of Kramatorsk in Donetsk. Oleksiy Biloshytskiy shared online footage, which could not be independently verified, of material burning fiercely underneath a pile of aggregate. “Another use of phosphorus ammunitions in Kramatorsk,” he said.

Zelenskiy will speak virtually at the Nato summit in Brussels on Thursday, where US president Joe Biden is also planning to push for new sanctions against Russia. “Three important summits are scheduled this week: G7, Nato and the EU,” he said. “New packages of sanctions, new support.”

About 300,000 people in the occupied southern city of Kherson are running out of food and medical supplies, a spokesperson for Ukraine’s foreign ministry said. Kherson was the first major Ukrainian city to fall into Russian hands since the invasion began on 24 February.

Russia plans to unleash a “great terror” on Kherson by kidnapping residents and taking them across the Russian border, an FSB whistleblower has claimed. The Kremlin was no longer willing to “play nicely” with protesters in the Ukrainian city, a letter said.

Russian forces have only three further days of fuel, food and ammunition left to conduct the war after a breakdown in their supply chains, Ukrainian military commanders have claimed. The statements were described as “plausible” by western officials although they said they were unable to corroborate the analysis.

Russian forces have “kidnapped” 2,389 children from the Russian-controlled territories of Luhansk and Donetsk, the US embassy in Kyiv has said, citing figures by Ukraine’s foreign ministry. The embassy said: “This is not assistance. It is kidnapping.”

At least one person has died after drones attacked a scientific institute in the capital, Kyiv, AFP reports. Rescuers were seen removing a body from the scene, as smoke rose from the seven-storey building at the Institute for Superhard Materials in north-west Kyiv, part of the National Academy of Science of Ukraine.

The Ukrainian health minister, Viktor Lyashko, said 10 hospitals had been completely destroyed since Russia invaded. Other hospitals could not be restocked with medicines and supplies because of nearby fighting, the minister added.

A Ukrainian journalist, Victoria Roshchyna, has been released from captivity by Russian forces, Ukrainian outlet Hromadske said. There is, however, growing concern about well-known photojournalist Maksym Levin, who was last reported to be on the frontline near Kyiv, but nobody has had any contact with him since 13 March.

The UN secretary general, Antonio Guterres, has said it is time for Russia to end its “absurd” and “unwinnable” war in Ukraine, as the EU prepared to set up a “trust fund” aimed at helping Kyiv repel the invasion and rebuild afterwards. Speaking to reporters at the UN’s headquarters in New York, Guterres said the war was “going nowhere, fast”.

The European Commission will set out plans on Wednesday for how people fleeing Ukraine will access jobs, education and housing in the EU, Reuters reports. Maroš Šefčovič, the commission’s vice-president, said the bloc must ensure the right resources are in place to meet people’s needs after initial efforts were focused on receiving people at the border.