Ukrainian forces were bolstering defences in key cities on Wednesday as Russia’s advance faltered amid fierce resistance in some areas, the general staff of Ukraine’s armed forces said, while the strategic port city of Mariupol remains encircled as a humanitarian crisis grows.

Across the country, thousands of people are thought to have been killed, both civilians and soldiers, in nearly two weeks of fighting.

Russian forces have seen their advances stopped in certain areas – including around Kyiv – by fiercer resistance than expected from the Ukrainians.

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Ukrainian soldiers in an armoured vehicle on the outskirts of Kyiv (Emilio Morenatti/AP)

Ukraine’s general staff said in a statement that it is building up defences in cities in the north, south and east, and that forces around the capital are resisting the Russian offensive with unspecified strikes and “holding the line”.

In the northern city of Chernihiv, Russian forces are placing military equipment among residential buildings and on farms, the Ukrainian general staff said. And in the south, it said Russians dressed in civilian clothes are advancing on the city of Mykolaiv.

It did not provide any details of new fighting.

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An elderly woman is carried in a shopping trolley after being evacuated from Irpin, on the outskirts of Kyiv (Vadim Ghird/AP)

On the diplomatic front, Russian Foreign Minister Sergei Lavrov was expected to fly to Turkey later on Wednesday, and meet Ukrainian Foreign Minister Dmytro Kuleba and Turkish Foreign Minister Mevlut Cavusoglu on Thursday, Mr Cavusoglu’s office said.

The trilateral meeting was to take place on the sidelines of a summit being hosted by Turkey, a member of Nato, but no further details were announced.

In Kyiv, back-to-back air alerts on Wednesday morning urged residents to get to bomb shelters as quickly as possible over fears of incoming Russian missiles. An all-clear was given for each alert soon afterward.

Such alerts are common, though irregular, keeping people on edge. Kyiv has been relatively quiet in recent days, though Russian artillery has pounded the outskirts.

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People rest in a subway station being used as a bomb shelter in Kyiv (Felipe Dana/AP)

Kyiv regional administration chief Oleksiy Kuleba said the crisis for civilians in the capital is growing, with the situation particularly critical in the suburbs.

“Russia is artificially creating a humanitarian crisis in the Kyiv region, frustrating the evacuation of people and continuing shelling and bombing small communities,” he said.

More than two million people have now fled Ukraine, according to the United Nations.

As Moscow’s forces have laid siege to Ukrainian cities, the fighting has thwarted attempts to create corridors to safely evacuate civilians.

One evacuation did appear successful, with Ukrainian authorities saying on Tuesday that 5,000 civilians, including 1,700 foreign students, had been taken out via a safe corridor from Sumy, an embattled north-eastern city of a quarter-million people.

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(PA Graphics)

That corridor was to reopen for 12 hours on Wednesday, with the buses that took people south-west to the city of Poltava the day before returning to pick up more refugees, regional administration chief Dmytro Zhyvytsky said.

Priority was being given to pregnant women, women with children, the elderly and the disabled.

Russia, which calls its invasion of Ukraine a “special military operation”, has focused official statements about the war almost exclusively on fighting and evacuations in the separatist-held regions, where Russian-backed forces have been fighting Ukraine’s military since 2014.

On Wednesday, Defence Ministry spokesman Major General Igor Konashenkov said Russian forces had thwarted a large-scale attack plot in the east, citing in a televised statement what he claimed was an intercepted Ukrainian National Guard document.

“The special military operation of the Russian armed forces, carried out since February 24, pre-empted and thwarted a large-scale offensive by strike groups of Ukrainian troops on the Luhansk and Donetsk People’s Republics, which are not controlled by Kyiv, in March of this year,” he said.

He did not address Russia’s shelling, air strikes and attacks on Ukrainian civilians or cities, Russian military casualties or any other aspect of its bogged-down campaign.

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(PA Graphics)

In the south, Russian troops have advanced deep along Ukraine’s coastline in what could establish a land bridge to Crimea, which Moscow seized from Ukraine in 2014.

The city of Mariupol has been surrounded by Russian soldiers for days and a humanitarian crisis is unfolding in the encircled city of 430,000.

Bodies lie in the streets of the city, which sits on the Asov Sea. Hungry people break into stores in search of food and melt snow for water. Thousands huddle in basements, trembling at the sound of Russian shells pounding their city.

“Why shouldn’t I cry?” Goma Janna demanded as she wept by the light of an oil lamp below ground, surrounded by women and children. “I want my home, I want my job. I’m so sad about people and about the city, the children.”

An attempt on Tuesday to evacuate civilians and deliver badly needed food, water and medicine through a designated safe corridor failed, with Ukrainian officials saying Russian forces had fired on the convoy before it reached the city.

Mariupol, said Ukrainian Deputy Prime Minister Iryna Vereshchuk, is in a “catastrophic situation.”

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People queue to receive humanitarian aid in Mariupol, (Evgeniy Maloletka/AP)

Natalia Mudrenko, the highest-ranking woman at Ukraine’s UN Mission, told the Security Council that the people of Mariupol have “been effectively taken hostage” by the siege.

Her voice shook with emotion as she described how a six-year-old girl died shortly after her mother was killed by Russian shelling. “She was alone in the last moments of her life,” she said.

Authorities in Mariupol plan to start digging mass graves for the dead. The shelling has shattered buildings, and the city has no water, heat, working sewage systems or phone service.

Theft of food, clothes, and even furniture, has become widespread, with locals referring to the practice as “getting a discount”. Some residents have been reduced to scooping water from streams.

With the electricity out, many people are relying on their car radios for information, picking up news from stations broadcast from areas controlled by Russian forces or Russian-backed separatists.

Ludmila Amelkina, who was walking along an alleyway strewn with rubble and walls pockmarked by gunfire, said the destruction has been devastating.

“We don’t have electricity, we don’t have anything to eat, we don’t have medicine. We’ve got nothing,” she said, looking skywards.

Ukrainian President Volodymyr Zelensky said efforts were under way to evacuate some 18,000 people from Kyiv and embattled towns near it.

He said on Wednesday the efforts are part of broader evacuation attempts by multiple humanitarian corridors within Ukraine, and warned Russian forces against violating cease-fire promises.

He appealed again for foreign air support, saying “send us planes”. Western powers have sent military equipment and beefed up forces on Ukraine’s eastern flank but have been wary of providing air support and getting drawn into a direct war with Russia.

He also issued an appeal, unusually in Russian, to urge Russian soldiers to leave.

“Our resistance for almost two weeks has shown you that we will not surrender, because this is our home. It is our families and children. We will fight until we can win back our land,” he said. “You can still save yourselves if you just go home.”