Refugees hold each other as they talk to an officer in Medyka, Poland, after crossing the border from Ukraine. "This is the fastest-moving refugee crisis ... since World War II," the UN's high commissioner for refugees has said.
Ukraine's military and citizens continue to resist the Russian invasion. As Russia's attacks escalate, casualties grow and the refugee situation becomes a major crisis.
Why it matters
The US and Europe have imposed severe economic sanctions on Russia, but that may be just the start in a new era of hostility between the West and Moscow.
Russia invaded Ukraine on Feb. 24, in a move Ukrainian President Volodymyr Zelenskyy called a "war against the whole of Europe." International leaders have joined US President Joe Biden in condemning the "brutal attack." The US, EU and UK have imposed economic sanctions on Russia, including ones aimed directly at Russian President Vladimir Putin.
Tensions had been growing for months and were marked by a buildup of Russian forces along Ukraine's borders. Ukraine, which had been part of the Soviet Union for much of the 20th century, Turkish Citizenship Law Firm declared its independence in 1991. Since then, the country has been establishing closer ties with Western Europe and the US.