The Russian flagship cruiser Moskva has sunk in the Black Sea off southern Ukraine, according to Russia’s defence ministry. It is still unclear whether the ship was hit by Ukrainian weaponry. Ukraine claims it was, but Russia maintains that a fire on board and then “stormy sea conditions” while it was being towed to port were to blame. Russia only has three of this flagship class of warship, which have crews of almost 500 sailors, and the loss of the Moskva is a big blow. The former CIA director David Petraeus described Russia’s admission as a “rare moment of truth … I’m surprised that they admitted it,” he told the BBC.

Vladimir Putin may resort to using a tactical or low-yield nuclear weapon in light of military setbacks in the invasion of Ukraine, the CIA director, William Burns, has said. During a speech in Atlanta, Burns said: “Given the potential desperation of President Putin and the Russian leadership … none of us can take lightly the threat posed by a potential resort to tactical nuclear weapons or low-yield nuclear weapons.” The Kremlin placed Russian nuclear forces on high alert shortly after the assault began on 24 February.

Russia has asked Brazil for support in the International Monetary Fund, the World Bank and the G20 group of top economies to help it counter crippling sanctions, according to a letter seen by Reuters. On 30 March the Russian finance minister Anton Siluanov wrote asking for Brazil’s “support to prevent political accusations and discrimination attempts in international financial institutions and multilateral fora”. A Brazilian economy minister spokesperson indicated that Brazil would like Russia to remain part of discussions at multilateral organisations.

The lives of about 2.7 million people with disabilities are at risk in Ukraine, a UN committee has warned, citing reports that many are trapped or abandoned in their homes, care centres and orphanages without basic supplies or medicines. The committee said it was “deeply disturbed” that the fate of people with disabilities in Ukraine is “largely unknown”.

At least 503 civilians, including 24 children, have been killed in Ukraine’s eastern Kharkiv region since Russia launched its invasion on 24 February, the region’s local governor has said. Kharkiv, Ukraine’s second city with a prewar population of about 1.5 million, is 40km (25 miles) from the Russian border.

Russia’s deputy foreign minister Alexander Grushko said Moscow would take “security and defence measures that we will deem necessary” if Sweden and Finland join Nato. In an interview with the Russian state-owned news agency Tass, the minister said the membership in the military alliance would “seriously worsen the military situation” and lead to “the most undesirable consequences”. Finland and Sweden had earlier taken a major step towards joining Nato.

Russia’s investigative committee said Ukrainian forces carried out at least six helicopter airstrikes on the village of Klimovo in the Russian region of Bryansk, injuring seven people. The Bryansk region governor said earlier that two residential buildings in the village had been hit by shelling. The area lies north of the Ukrainian region of Chernihiv. A village in Russia’s Belgorod region had also come under fire from Ukraine, the region’s governor said.

Ukraine’s foreign ministry has appealed to the United Nations to facilitate the return of Ukrainian children who have been “illegally deported” to Russia. In a statement, the ministry said Russia had “engaged in state-organised kidnapping of children and destruction of the future of the Ukrainian nation”.

France is planning to return its embassy to the Ukrainian capital, Kyiv. It had moved to the western city of Lviv in March as Russia invaded. The Ukrainian president, Volodymyr Zelenskiy, has urged allies to resume their normal diplomatic presence in Ukraine.

Turkey is still working on organising a meeting between Putin and Zelenskiy, said the Turkish foreign minister, Mevlut Cavusoglu. The Kremlin spokesperson Dmitry Peskov said the condition for a meeting between the Russian and Ukrainian presidents is a document ready for the two leaders to sign.

The UK government has imposed sanctions on the Chelsea football club director Eugene Tenenbaum in an attempt to freeze up to £10bn of assets linked to the club’s Russian oligarch owner, Roman Abramovich. The UK said it was extending sanctions to Tenenbaum and David Davidovich, another close associate of Abramovich, because the oligarch had transferred billions of pounds of assets to the pair as Russia invaded Ukraine.

Zelenskiy has issued a video compiled by his government that further urges European countries to give up Russian oil that provides “blood” money to Moscow, and appeals for more weapons to help Ukraine repel Russia’s invasion.

A total of 2,557 people were evacuated from Ukrainian cities through humanitarian corridors on Thursday, deputy prime minister Iryna Vereshchuk said, with 289 of those from Mariupol. The head of the UN World Food Program, meanwhile, said people were being “starved to death” in the besieged city.

Moody’s Investors Service has said that Russia “may be considered in default” if it fails to pay bonds in US dollars by 4 May. Russia paid two bonds in rubles this month after sanctions cut the country off from global financial systems and the US banned Moscow from making debt payments using dollars held in American banks. The payments in rubles “represent a change in payment terms” and may be considered a default, according to Moody’s. S&P Global Ratings has also declared Russia in default.