The fourth round of negotiations between Russia and Ukraine resumed on Tuesday via video link, a day after the two sides announced a break for a "technical pause."

The Kremlin said Tuesday it was too soon to draw any conclusions from the talks to resolve the conflict.

"The work is complex, but the very fact that the work is continuing is in itself positive," Kremlin spokesman Dmitry Peskov told reporters. "We don't want to give any forecasts. Let's wait for tangible results," he said.

One of Ukrainian President Volodymyr Zelenskyy's top aides said late on Monday that the fighting would be over by May – and could even end within weeks.

"I think that no later than in May, early May, we should have a peace agreement, maybe much earlier, we will see, I am talking about the latest possible dates," Oleksiy Arestovich said in a video published by several Ukrainian media outlets.

Delegations from Moscow and Kyiv have met for four rounds of talks to find a diplomatic resolution to the nearly three weeks of fighting between Russia and Ukraine.

Both sides indicated over the weekend that they were making headway. Russia's negotiators hailed "significant progress" while a lead Ukrainian negotiator said Moscow's delegation had stopped issuing "ultimatums" and instead "carefully listens to our positions."

Kyiv to impose a 35-hour curfew

Kyiv will impose a 35-hour curfew from Tuesday night amid a "difficult and dangerous moment" after several Russian strikes, Mayor Vitali Klitschko said.

The curfew from 8:00 p.m. (1800 GMT) on Tuesday until 7:00 a.m. (0500 GMT) on Thursday was a "decision of the military command," he said.

It comes as the Polish, Czech and Slovenian prime ministers were travelling to Kyiv by train on Tuesday in the first visit by foreign leaders to the capital.

Polish Prime Minister Mateusz Morawiecki said the trip was "to confirm the unequivocal support of the entire European Union for the sovereignty and independence of Ukraine."

Britain on Tuesday imposed an additional 35 percent tariff on a swathe of Russian imports, including steel, wood, cereals, drinks, fur and white fish. The list of goods covered by the additional tariffs is worth $1.2 billion a year.

Britain will also deny Russia and Belarus access to "most favored nation" tariffs under World Trade Organization rules.

More than 3 million refugees

More than 3 million people have fled Ukraine since February 24, nearly half of them minors, with a child becoming a refugee every second, the UN said.

"We have now reached the 3 million mark in terms of movement of people out of Ukraine," Paul Dillon, a spokesman for the International Organization for Migration (IOM) of the United Nations, told reporters.

"Three million lives uprooted. Three million women, children and vulnerable people separated from their loved ones," IOM chief Antonio Vitorino said in a tweet. "We need an immediate cessation of hostilities."

The UN refugee agency, UNHCR, meanwhile put the total number of refugees to date at 2,969,600. More than half of them, 1.8 million, have fled to Poland, it said.

(With input from agencies)

(Cover: In this handout photo released by BelTA, flags are seen on a table before Russian-Ukrainian talks in Belarus, March 7, 2022. /CFP)