The United Nations said Monday it will need $4.2 billion to provide humanitarian aid in Ukraine in 2024, and to help millions of refugees who have fled the war-torn country.

While the Gaza war has dominated headlines in recent months, Russia's war in Ukraine is set to enter its third year in February.

The UN hopes to reach 8.5 million people within Ukraine and 2.3 million refugees and their host communities in eastern Europe.

"A recent wave of attacks underscores the devastating civilian cost of the war, while a bitter winter is ratcheting up the urgent need for life-saving humanitarian aid," the UN said.

The full-scale Russian invasion in February 2022 was the biggest invasion of a European country since World War II and the largest refugee crisis faced by the continent since the 1939-1945 conflict.

The UN says 14.6 million people will need humanitarian assistance in Ukraine this year -- 40 percent of the population -- of which it will try to reach the 8.5 million most in need.

"Hundreds of thousands of children live in communities on the front lines of the war, terrified, traumatised and deprived of their basic needs," UN aid chief Martin Griffiths said in a statement.

"That fact alone should compel us to do everything we can to bring more humanitarian assistance to Ukraine.

"Homes, schools and hospitals are repeatedly hit, as are water, gas and power systems. The very fabric of society is under attack with devastating consequences."

- 6.3 million refugees -

Griffiths and the UN High Commissioner for Refugees, Filippo Grandi, launched the plan at a joint press conference at the UN's Palais des Nations in Geneva.

Some 6.3 million people have fled Ukraine and remain refugees, mostly across Europe.

The regional refugee response plan is seeking $1.1 billion and targets reaching 2.3 million refugees and host communities.

"Millions of refugees from Ukraine still need urgent support," Grandi insisted.

Only half of school-age Ukrainian refugee children are enrolled in schools in host countries, said the UN, while a quarter of refugees in need struggle to access health care.

Only 40 to 60 percent are employed, it said -- often below their qualifications -- while many remain vulnerable with no means to support themselves.

"Host countries continue to extend protection and include them in society, but many vulnerable refugees still need help. They shouldn't feel pressed to return because they cannot make ends meet in exile," said Grandi.

"All refugees must be helped and given opportunities to use and build their talents to prepare them for eventual voluntary return when the situation allows."

- Focus on hardest-hit -

The 2023 humanitarian response plan for within Ukraine sought $3.9 billion and was 64 percent funded.

The UN said that despite access challenges -- particularly to areas occupied by Russian forces -- aid workers reached 10.5 million people in Ukraine in 2023.

In its global humanitarian appeals this year, the UN has tried to rein in its objectives, seeking to prioritise those in need with smaller appeals -- in the hope that they will be more reliably funded.

This year is asking for $3.1 billion.

"The response strategy in 2024 focuses on the people with the most severe humanitarian needs across the country, particularly those in the front-line," the UN said.

Russia has intensified its aerial assaults on Ukraine in recent weeks. Bolstering its arsenal, it has geared up for a long war and reoriented its economy.