Russia said its forces had stopped firing near two besieged Ukrainian cities on Saturday to allow safe passage to civilians fleeing fighting, but city officials said Moscow was not fully observing the partial ceasefire.

The Russian defence ministry said its units had opened humanitarian corridors near the cities of Mariupol and Volnovakha which were encircled by its troops, Russia's RIA news agency reported.

In Mariupol, citizens would be allowed to leave during a five-hour window, it quoted the city's officials as saying, as Russia's invasion of Ukraine entered into its 10th day.

The southeastern port city has come under heavy bombardment, a sign of its strategic value to Moscow due to its position between Russian-backed separatist territory in east Ukraine and the Crimean peninsula, which Moscow seized from Ukraine in 2014.

"This night the shelling was harder and closer," a staff member from Doctors without Borders/Medecins sans Frontieres (MSF) said, according to the aid agency, adding there was still no power, water, heating or mobile phone links and food was scarce.

The Ukrainian government said the plan was to evacuate around 200,000 people from Mariupol and 15,000 from Volnovakha, and the Red Cross is the ceasefire's guarantor.

But the city council later said Russia was not observing the ceasefire entirely. "We are negotiating with the Russian side to confirm the ceasefire along the entire evacuation route," it said. There was no direct response from the Russian side.

Ukraine's government was looking into reports from its military that the Russian troops were using the ceasefire to advance towards Mariupol, Ukraine's Minister for Reintegration of Temporary Occupied Territories, Iryna Vereshchuk, said.

The Russian defence ministry said a broad offensive would continue in Ukraine, where it denies targeting civilians.

"The armed forces of the Russian Federation continued to carry out strikes on the military infrastructure of Ukraine," Defence Ministry spokesman Igor Konashenkov said, adding that forces from separatist-held Donetsk in Ukraine's east were continuing to tighten the encirclement of Mariupol.

Mariupol city authorities urged civilians to leave.

"We are simply being destroyed," Mariupol Mayor Vadym Boychenko said.

Aid agencies have warned of a humanitarian disaster across the country as food, water and medical supplies run short. More than 1.2 million refugees have fled to neighbouring European countries, the United Nations refugee agency said on Saturday.

President Vladimir Putin launched the invasion on Feb. 24 after weeks of massing troops near Ukraine and his actions have drawn almost universal condemnation around the world. Officials in Ukraine have reported thousands of dead and wounded civilians and many countries have imposed heavy sanctions on Russia.

Moscow says its aim is to disarm its neighbour, counter what it views as NATO aggression and capture leaders it calls neo-Nazis.

NO TO NO-FLY ZONES

Ukraine says Russian forces have focussed efforts on encircling Kyiv and Kharkiv, the second-biggest city, while aiming to establish a land bridge to Crimea.

Kyiv, in the path of a Russian armoured column that has been stalled outside the Ukrainian capital for days, was again under attack, with explosions audible from the city centre.

Ukrainian media outlet Suspilne cited authorities in Sumy, about 300 km (190 miles) east of Kyiv, as saying that there is a risk of fighting in the city's streets, urging residents to stay in shelters.

Ukrainian President Volodymyr Zelenskiy was expected to press Washington for more help in a video call with the U.S. Senate at 9:30 a.m. ET (1430 GMT) on Saturday.

At a meeting on Friday, NATO allies rejected Ukraine's appeal for no-fly zones, saying they were increasing support but that stepping in directly could make the situation worse.

"We have a responsibility ... to prevent this war from escalating beyond Ukraine because that would be even more dangerous, more devastating and would cause even more human suffering," said NATO Secretary-General Jens Stoltenberg.

Zelenskiy slammed the summit, saying "It was clear that not everyone considers the battle for Europe's freedom to be the number one goal".

The United States is weighing cuts to imports of Russian oil and ways to minimise the impact on global supplies and consumers as lawmakers fast-track a bill that would ban Russian energy imports. Global oil prices surged over 20% this week on concern about supply shortages, posing a risk to global economic growth.

FIERCE DEFENSE

Ukraine's Defence Minister Oleksii Reznikov said 66,224 Ukrainian men had returned from abroad to join the fight against Russia's invasion. "These are 12 more combat and motivated brigades! Ukrainians, we are invincible," he said in an online post.

Ukraine's military said armed forces "are fighting fiercely to liberate Ukrainian cities from Russian occupiers," counterattacking in some areas and disrupting communications.

"Units of the invaders are demoralized, soldiers and officers of the occupying army continue to surrender, flee, leaving weapons and equipment on Ukrainian soil," it said, adding that at least 39 Russian planes and 40 helicopters had been destroyed.

Russia said it had destroyed 82 Ukrainian aircraft, 708 armoured vehicles, 74 multiple rocket launchers and 56 drones.

Reuters has not been able to independently verify such accounts from either side.

Thousands of people waited for hours on Friday outside the railway station at the western city of Lviv to board trains heading to Poland. Families arrived with few belongings. Some were in wheelchairs, others accompanied by pet dogs and cats, uncertain about their fate.

"All we took with us is the bare necessities," said Yana Tebyakina. "A change of clothes. That's it. All the rest we left behind, all our lives stayed back at home." 

Russian forces have made their biggest advances in the south, where they captured their first sizeable Ukrainian city, Kherson, this week. Bombing has worsened in recent days in the northeast cities of Kharkiv and Chernihiv.

Russia's parliament passed a law on Friday imposing a prison term of up to 15 years for spreading intentionally "fake" news about the military.

"This law will force punishment - and very tough punishment - on those who lied and made statements which discredited our armed forces," said Vyacheslav Volodin, the chairman of the Duma, Russia's lower house of parliament.

Russia is blocking Facebook for restricting state-backed channels and the websites of the BBC, Deutsche Welle and Voice of America.

Reuters