More than 870,000 people, who fled abroad since the Russian invasion on February 24, have now returned to Ukraine amid concerns about worsening food security inside the country, according to the United Nations (UN). Citing the State Border Guard Service, the UN aid coordination office, OCHA, said 30,000 people are crossing back into Ukraine every day. The recent returnees reportedly include women with children and older persons, compared to men mostly at the beginning of the escalation. "This significant figure suggests that migration back to Ukraine might continue increasing, potentially creating new challenges for the humanitarian response as people will need support to reintegrate into their communities or find suitable host communities if returning to their homes is no longer viable," the OCHA said. Of the 12 million people in need in Ukraine, humanitarians have reached 2.1 million of them, and the UN's $1.1 billion flash appeal for Ukraine is now 64 percent funded. Read: Russia loses warship, says attacks on Kyiv will increase Fighting is now concentrated in the eastern and southern Ukraine, causing damage and civilian casualties and driving humanitarian needs. In its latest emergency update, the OCHA reported that two humanitarian workers and five of their relatives had been killed in eastern Donetsk oblast. They were sheltering at the Caritas Mariupol office when the building was reportedly hit by rounds fired from a tank, probably on March 15, although the information only became available recently, as the city had been cut off for weeks. "Tens of thousands of civilians in Mariupol – which has been an epicentre of horror since the conflict began – and in other locations around Ukraine have now endured 50 days of violence and shelling. More than 1,932 civilians have died since 24 February, including more than 150 children," UN Emergency Relief Coordinator Martin Griffiths said. Meanwhile, the Food and Agriculture Organization (FAO) said there are "immediate food insecurity issues" in nearly three in 10 regions – with a further 11 percent of regions (that are partially exposed to fighting) expecting shortages within two months. Rural and isolated communities have been hit hardest by food insecurity, FAO said, as it announced support for farmers to plant their fields, save livestock and produce food. Read: IMF chief: Ukraine war and inflation threaten global economy Urgent cash support is also planned for the most vulnerable families, including those headed by women, the elderly and those with disabilities. Meanwhile, the OCHA also noted that Russia reported that more than 783,000 people – including nearly 150,000 children – crossed into Russia from Ukraine since 24 February. The latest data from the UN refugee agency, UNHCR, indicates that more than 4.7 million people have fled Ukraine since the war began. Another seven million are internally displaced.