UN: 3.5 million have fled Ukraine since start of invasion

The United Nations (U.N.) on Tuesday said that 3.5 million people have fled Ukraine since the Russian assault on the nation began almost four weeks ago.

The U.N. refugee agency gave the estimate on Tuesday, noting that another 6.5 million people are thought to have been displaced inside Ukraine, The Associated Press reported.

Countries surrounding Ukraine have taken in the most refugees, with Poland taking more than half at more than 2.1 million.

Other European countries such as Ireland have begun lifting visa requirements for Ukrainians so they could more easily travel outside Poland, Romania and Moldova.

The United Kingdom is paying residents money to host Ukrainian refugees who flee to their country.

Most of the refugees are women and children since men are not allowed to leave Ukraine under martial law.

The United Nations Children's Fund (UNICEF) said last week more than 1.5 million children have left the country since the start of the war.

"The war in Ukraine is leading to massive displacement and refugee flows - conditions that could lead to a significant spike in human trafficking and an acute child protection crisis," Afshan Khan, UNICEF's regional director for Europe and Central Asia, said.

"Displaced children are extremely vulnerable to being separated from their families, exploited, and trafficked. They need governments in the region to step up and put measures in place to keep them safe."