Ukraine’s president, Volodymyr Zelenskiy, has warned his country “does not have time to wait” while pushing for an oil embargo on Russia in his latest national address. He also said he is committed to pressing for peace despite Russian attacks on civilians that have stunned the world, and renewed his plea for countries to send more weapons ahead of an expected surge in fighting in the country’s east.

Zelenskiy said his country is ready for a tough battle with Russian forces amassing in the east of the country. “This will be a hard battle; we believe in this fight and our victory. We are ready to simultaneously fight and look for diplomatic ways to put an end to this war.”

The British prime minister, Boris Johnson, pledged a major new infusion of British arms and financial aid during a surprise trip to Kyiv on Saturday. Johnson said the UK and its partners and allies will provide support so that “Ukraine will never be invaded again”. The UK confirmed it will send 120 armoured vehicles and new anti-ship missile systems.

Johnson praised Zelenskiy’s “resolute leadership and the invincible heroism”. “Putin’s monstrous aims are being thwarted,” Johnson said. The reputations of the Russian president, Vladimir Putin, and his government have been “permanently polluted” by war crimes against civilians in Ukraine, he added.

Russia’s withdrawal from northern Ukraine has left evidence of “disproportionate targeting” of civilians, mass graves, the use of hostages as human shields, according to the latest British intelligence report. The report also claimed Russian forces continue to use improvised explosive devices (IEDs) to inflict casualties, lower Ukrainian morale and restrict freedom of movement.

Five people have been killed in east Ukraine shelling, according to the Donetsk governor. Four were reported killed in the city of Vugledar, and one in the town of Novomikhaylovka.

In the town of Borodianka, north-west of Kyiv, rescue teams sorted through the rubble of houses destroyed in Russian bombardments, looking for those missing. Heavy Russian bombardment has razed residential buildings and Ukrainian authorities are attempting search, clear-up and, hopefully, some rescue activities.

Ukraine carried out a prisoner exchange with Russia on Saturday, the third such swap since the start of the war, with 12 soldiers confirmed to be coming home, the Ukrainian deputy prime minister, Iryna Vereshchuk, wrote online.

A total of 4,553 people were evacuated from Ukrainian cities through humanitarian corridors on Saturday, fewer than the 6,665 who escaped on Friday, Vereshchuk said. Ten humanitarian corridors to evacuate people from embattled areas across the country had been agreed on Saturday.

The European Commission is pledging €1bn to support Ukraine and countries receiving refugees fleeing the war following Russia’s invasion, said the commission’s president, Ursula von der Leyen.

The Czech Republic has delivered tanks, multiple-rocket launchers, howitzers and infantry fighting vehicles to Ukraine among military shipments that have reached hundreds of millions of dollars and will continue, two Czech defence sources told Reuters.

The Austrian chancellor, Karl Nehammer, met Zelenskiy earlier on Saturday, following a visit to the city of Bucha to the north-west of Kyiv, where mass civilian graves and street killings by Russian forces were discovered last week.

Russia has reorganised the command of its battle operations in Ukraine, installing a new general with extensive experience in Russian operations in Syria, according to a western official. The commander of Russia’s southern military district, Gen Alexander Dvornikov, now leads the invasion, the source told the BBC, adding: “We would expect the overall command and control to improve.”