Buses transported civilians out of one besieged Ukrainian city and supplies to another on Tuesday, as officials attempted to move people away from a Russian onslaught and alleviate the dire humanitarian situation for those who remained trapped. However, reports of renewed Russian attacks on the Mariupol port threatened to derail the efforts once more.

On the 13th day of the invasion, Europe’s worst refugee crisis since World War II worsened, with UN officials reporting that 2 million people had fled Ukraine.

Demand for safe evacuation routes for civilians has increased in tandem with Russian forces’ intensifying shelling, which has resulted in significant advances in southern Ukraine but has stalled in other areas. Attempts to establish cease-fires along humanitarian corridors have repeatedly failed in the face of Russian shelling.

The United Nations Human Rights Office has recorded over 400 civilian deaths since the invasion began, but the true number is much higher, according to the organization. In addition to the humanitarian disaster unfolding in Ukraine, the fighting has caused global energy prices to skyrocket and stockpiles to plummet, threatening the food supply and livelihoods of people all over the world who rely on crops grown in the fertile Black Sea region.

Western countries have condemned the invasion and sought to arm Ukraine while also sanctioning Vladimir Putin’s Russia. The measures have harmed the Russian economy by causing companies to withdraw from or drastically reduce their operations in the country. Shell announced Tuesday that it would no longer purchase oil and natural gas from the country, further emphasizing the country’s economic isolation.

According to video from the Ukrainian communications agency, a convoy of buses packed with people moved along a snowy road from the northeastern city of Sumy on Tuesday. According to Ukrainian Deputy Prime Minister Iryna Vereshchuk, the group was headed southwest to the Ukrainian city of Poltava and included students from India and China.

Meanwhile, buses bearing red cross symbols and carrying water, basic food staples, and medicines made their way toward the besieged southern port of Mariupol, scene of some of the war’s worst desperation. According to Vereshchuk, the vehicles will then ferry civilians out of the city.

However, shortly after officials announced that buses were on their way, the Ukrainian president’s office announced that it had been informed of shelling on the escape route. It is unclear whether the supply convoy arrived in Mariupol, or whether civilians will be allowed to board the buses if the shelling continues.

The governor of the Kyiv region, Oleksiy Kuleba, said Ukraine was also making plans to get people out of the Irpin suburb, though it was unclear whether this would be along one of the five official corridors promised by the Russians.

Zelenskyy accused the International Red Cross of “forbidding the use of its emblem on our cars,” but he didn’t elaborate. Videos of buses leaving Sumy and heading toward Mariupol show signs with a red cross on the side, but it’s unclear who put them there.

According to the general staff, “demoralized” Russian forces are looting in areas they have occupied, commandeering civilian buildings such as farm hangars for military equipment, and establishing firing positions in populated areas. The claims were unable to be independently verified.

Soldiers and volunteers in Kyiv have constructed hundreds of checkpoints to protect the city of nearly 4 million people, frequently using sandbags, stacked tires, and spiked cables. Some barricades appeared substantial, with heavy concrete slabs and sandbags stacked more than two stories high, while others appeared haphazard, with hundreds of books used to weigh down stacks of tires. On Monday, Moscow issued a new set of demands to halt the invasion, including that Ukraine recognize Crimea as part of Russia and that the eastern regions controlled by Moscow-backed separatist fighters be recognized as independent. It also demanded that Ukraine amend its constitution to ensure that it does not join international organizations such as NATO and the EU. These demands have already been rejected by Ukraine.