UNITED NATIONS, April 14 (Xinhua) -- The United Nations on Tuesday marked the third anniversary of the Sudanese civil war with a warning that the world's worst humanitarian crisis is deepening.

UN Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator Tom Fletcher said Sudan remains the world's largest humanitarian crisis.

"Nearly 34 million people in Sudan -- or almost two out of every three people -- need humanitarian assistance, as hunger tightens its grip, children face acute malnutrition and women and girls are subjected to widespread and brutal violence," Fletcher said.

The UN relief chief called for urgent action to stop the fighting, protect civilians, ensure safe and unimpeded humanitarian access, and mobilize the funding needed to sustain life-saving operations.

UN Women said the number of women and girls requiring support after experiencing gender-based violence nearly doubled in two years and quadrupled since the start of the war.

"Women and girls are being raped and killed in their homes, and as they flee, seek food, water and medical care," said UN Women Regional Director for East and Southern Africa Anna Mutavati. "The use of sexual violence has been embedded in the blueprint of Sudan's war."

UN Women cited a new Gender Alert on the war, published Tuesday, as saying that more than 4.3 million women and girls have been displaced in Sudan, while 17.1 million require humanitarian assistance. For many, there is limited or no access to food, shelter or medical care.

Eva Hinds, UN Children's Fund (UNICEF) chief of communication in Sudan, said that at least 245 children were reportedly killed or injured in just the first three months of this year.

"This is a sharp increase compared to the same period last year. Most of these children killed or injured were in Darfur and the Kordofan states, where violence has become a constant part of daily life," Hinds told a press briefing in Geneva.

She said that "since the war began, the United Nations has verified more than 5,700 grave violations against children across Sudan. More than 4,300 children have been killed or maimed, with Darfur and Kordofan states again accounting for the highest numbers."

Humanitarian access remains a major challenge, since large parts of the country are still cut off because of fighting, damaged infrastructure, and administrative obstacles. The constraints are especially severe in Darfur, Kordofan and parts of Blue Nile state, leaving many of the most vulnerable children beyond reach, said Hinds.

UNICEF Executive Director Catherine Russell said: "For three years, children across Sudan have been killed, injured, and displaced at staggering levels. Their homes, schools and hospitals continue to come under attack. There is no justification for violence against children. It reflects a collective failure by parties to the conflict to protect the most basic rights of children."

The UN Office for the Coordination of Humanitarian Affairs (OCHA) said that drone strikes have reportedly killed nearly 700 civilians in the first three months of this year. On Monday, a drone strike in Ed Daein, East Darfur state, reportedly killed nine civilians and injured 27 others, including a child and health-affiliated workers.

OCHA reiterated that the violence must stop.

"Civilians and civilian infrastructure must be protected in line with international humanitarian law," said the office. "Humanitarian access must be rapid, safe, unimpeded and sustained, and the response must be fully funded to save lives."

Fletcher also said the grim and chastening anniversary marks another year when the world has failed to meet the test of Sudan. ■