UNITED NATIONS (AP) — The United Nations paid tribute on World Humanitarian Day to the thousands of aid workers who have been killed, injured, assaulted and kidnapped, saying the world has become a more dangerous place for those who risk their lives to help people in need.

U.N. deputy humanitarian chief Ursula Mueller told a news conference Monday that last year was the worst in five years for violence against aid workers and the second worst on record.

In 2018, there were 131 aid workers killed, 144 wounded and 130 kidnapped "in 35 crisis-affected countries," she said. And so far in 2019, some 57 have been killed, 59 wounded and 40 kidnapped.

"Humanitarian work is getting more dangerous due to the erosion of respect for international law, international humanitarian law, international human rights law," Mueller said. "As respect for the laws of war weakens around the world, aid workers are increasingly vulnerable when they are more needed than ever before."

World Humanitarian Day is held annually on Aug. 19, and 2019 marks the 10th anniversary of its observance. It is the day of the worst terrorist attack against the United Nations, when the Canal Hotel in Baghdad where the U.N. had its headquarters was bombed in 2003, killing 22 U.N. staff members including the mission head, Sergio Viera de Mello, a former U.N. humanitarian chief.

U.N. Deputy Secretary-General Amina Mohammed spoke at a ceremony Monday morning before the tattered U.N. flag salvaged from the Baghdad headquarters saying "across the years since, so many others have perished in the line of duty, on the front lines of crisis and in epicenters of dire need."

In their honor, over a hundred U.N. staff members and diplomats at the ceremony observed a minute of silence.

Mueller said that since the Baghdad bombing, "more than 4,500 aid workers have been killed, injured, detained, assaulted or kidnapped while carrying out their work."

"That is equivalent to 280 humanitarians attacked every year," she said. "That is too many of our colleagues and fellow humanitarians killed or injured, and too many making the ultimate sacrifice."

Mohammed said the U.N. is changing the way it operates around the world, strengthening safety and security measures, providing preparedness training, instituting rapid response measures and increasing counseling and mental health support.

"Those who attack the United Nations want to make us afraid, feel weak, and to retreat," she said. "Those we honor today inspire us to be bold and determined and to go forward."