IRAQ/UN: Mrs Mary Robinson, Mr Sergio Vieira de Mello's predecessor at the United Nations, said she was "very shocked and devastated" by the Baghdad attack, which, she said, showed the need for a wider mandate for the UN.
The former President told the BBC: "It is a huge blow but curiously I think it may bring home the need for a broader and more rounded UN mandate on the ground and more countries involved.
"It is extraordinarily important that Iraq does not descend into a situation of complete lack of security and a worse situation for the civilian population of Iraq.
"It is an appalling blow and the world must rally not just the coalition, the occupation forces that are in Iraq at the moment, the United States, Britain and others but also France, Germany, India, Brazil, South Africa, all the countries of the world must now respond, I think, appropriately.
"There has to be real desire to change the terms on the ground in Iraq and I think that can only be done by strong leadership, UN mandate and presence on the ground. There should be a leadership role for the United Nations."
Amnesty International's Secretary General, Ms Irene Khan, said: "The next few days in Iraq will be critical."