Two million people have fled Ukraine since Russia’s invasion the United Nations refugee chief and the International Organization for Migration said on Tuesday.

U.N. High Commissioner for Refugees,Filippo Grandi, confirmed the figure as more headed for the borders. Poland has received more than 1.2 million Ukrainian refugees, the most of any nation, U.N. figures show.

Civilians in one eastern Ukrainian city were shown leaving on buses Tuesday amid a a 12-hour-long cease-fire there after Russia and Ukraine agreed on establishing five safe corridors for people to escape the fighting.

Meanwhile, Russian aircraft continued to bomb cities in eastern and central Ukraine overnight, Ukrainian officials said. Shelling pounded suburbs of the capital, Kyiv.

Ukrainian President Volodymyr Zelenskyy urged his people to keep resisting the assault. Ukraine’s foreign minister says more than 20,000 people from 52 countries have volunteered to fight in Ukraine.

As the war enters its 13th day, food, water, heat and medicine have grown increasingly scarce in multiple cities facing electricity outages.

Here’s a look at key things to know about the war:

HAS THERE BEEN PROGRESS ON SAFE EVACUATIONS?

Videos Tuesday showed people boarding buses, and multiple buses marked with a red cross driving along a snowy road as the eastern city of Sumy was given a safe corridor for evacuation.

Ukrainian Deputy Prime Minister Iryna Vereshchuk said Tuesday both sides agreed to a cease-fire from 9 a.m. to 9 p.m Ukraine time for the evacuation of civilians from Sumy. Those leaving include foreign students from India and China, she said.

The Russian Defense Ministry has said civilians will be allowed to also leave the cities of Mariupol and the capital, Kyiv, where people have built hundreds of checkpoints to protect the city of nearly 4 million people.

Most of the corridors for fleeing civilians, however, will lead to Russia either directly or via Belarus, according to officials in Moscow. Russia’s ambassador to the U.N. suggested that humanitarian paths leading from the capital and other cities could give people a choice in where they want to go.

The safe corridors were agreed on by Ukrainian and Russian officials during their third round of direct talks Monday since the start of invasion Feb. 24. The foreign ministers of both countries are scheduled to meet in Turkey on Thursday, according to that country’s top diplomat.

WHAT ELSE IS HAPPENING ON THE GROUND?

Russian aircraft bombed cities in eastern and central Ukraine overnight, Ukrainian officials said. Shelling pounded suburbs of the capital, Kyiv. Bombs also hit oil depots in two other towns.

Ukraine’s Interior Ministry reported Tuesday that nine people, including two children, were killed in a Russian airstrike in Sumy on Monday.

The mayor of Lviv said the city in far western Ukraine is struggling to feed and house the tens of thousands of people who have fled there from other parts of the country. More than 200,000 Ukrainians displaced from their homes are now in Lviv, filling up sport halls, schools, hospitals and church buildings.

In the southern port city of Mariupol, an estimated 200,000 people — nearly half its population — are hoping to flee as hospitals there face severe shortages of antibiotics and painkillers. An official with Ukraine’s presidential office says humanitarian aid is being sent to the city.

A Russian general was killed in the fighting in Ukraine’s second-largest city, according to the Ukrainian military intelligence agency. He is the second Russian general reportedly killed since the invasion began. The report said he had fought with Russian forces in Syria and Chechnya and had taken part in the seizure of Crimea in 2014. It was not possible to confirm the death independently. Russia has not commented.

Russian troops have overall made significant advances in southern Ukraine but stalled in some other regions.

HOW MANY PEOPLE HAVE BEEN KILLED?

The death toll of the conflict has been difficult to measure. The U.N. human rights office said Monday that it had confirmed the deaths of 406 civilians and wounding of 801 others through the end of Sunday. However, it acknowledged the actual figures are likely considerably higher.

The World Health Organization said six health care workers have been killed and nearly a dozen wounded in attacks. It has confirmed 16 attacks on health care facilities in Ukraine since Russia’s invasion began.

Ukrainian refugees continue to pour into neighboring countries, including Poland, Romania and Moldova. Among them are an unknown number of people with U.S. citizenship, though some haven’t been able to flee Ukraine yet.

WHAT IS THE GLOBAL IMPACT?

Surging prices for oil and other vital commodities, such as wheat used in subsidized bread and noodles, are rattling global markets.

Worries are growing that Russia’s invasion of Ukraine will upend already tight supplies of oil. Russia is one of the world’s largest energy producers, with prices surging even further by the possibility the U.S. might bar crude imports from Russia.

A growing number of multinational businesses have cut Russia off from vital financial services, technology and a variety of consumer products in response to Western economic sanctions. Among those suspending services in Russia is Netflix, the popular streaming service.

In the Middle East, the war in Ukraine is magnifying divisions in the region following Moscow’s role in recent years in the war in Syria. Russia has support among militant factions in Lebanon, Iraq and Yemen where ally, Iran, has influence.

Despite countries sending weapons and military equipment to Ukrainian forces fighting the Russians, Western countries have rejected Ukrainian calls to impose a no-fly zone over the country. There are concerns such a move would risk dramatically escalating the conflict.