The top UN official for humanitarian aid, Valerie Amos, who oversaw international relief efforts in Syria and other trouble spots, is stepping down, Secretary General Ban Ki-moon said Wednesday.
Amos had been in the key post for more than four years, overseeing major aid operations in Syria as well as in South Sudan, Iraq and the Central African Republic.
Her departure comes as the United Nations is struggling to cope with a record 50 million people displaced from conflict.
Amos will stay on in her post as under-secretary general for humanitarian affairs and emergency relief coordinator until March.
No reason was given for her departure, but a UN official told AFP "she feels it's time to move on" after having been in the position since August 2010.
Ban expressed gratitude and praised Amos for the extensive experience she brought to the post.
She "has helped find solutions for people who are facing the worst experiences of their lives," he said in a statement.
The 60-year-old former British minister for international development "has tirelessly advocated for people around the world affected by disaster and conflict. For her, people have always come first," he said.
The announcement came the day after Amos reported to the UN Security Council on efforts to bring humanitarian aid to civilians in Syria, which has been torn by war for nearly four years.
Amos appealed for more cross-border aid deliveries and urged the 15-member council to push Damascus and all sides toward a political solution.
"I hope, for the sake of the people of Syria, that one is found soon," she told them.
There are more than 7.6 million people displaced inside Syria and 3.2 million others have fled the country.
"This is the largest number of people displaced from conflict in the world," she said.
Born in Guyana, Amos has been a lifelong campaigner for human rights and particularly vocal on issues related to Africa.
She was a minister for Africa from 2001 to 2003, in the government of former prime minister Tony Blair, and was chair of the Royal African Society from 2007 to 2009.
She also served as president of the privy council, leader of the House of Lords and British high commissioner to Australia.
Amos, who holds the title of baroness, was the first black woman to sit in the British cabinet following her appointment as international development secretary in 2003.