“The vicious acts that have been perpetrated against your country have cut us all to the core, for they are an attack on humanity itself,” wrote Mr. Annan in a letter to President Bush, sent on Wednesday. “The United Nations grieves with other New Yorkers, and expresses its solidarity with the American Government and people in this hour of trial.” Underscoring that terrorism threatened democracy, the rule of law, human rights and stability, the Secretary-General said all nations of the world must now work together to identify the perpetrators of these acts and bring them to justice. “All of us must renew our efforts to eradicate terrorism from the face of the earth,” he wrote. In his letter to Mayor Giuliani, Mr. Annan said that the UN was grieving with other New Yorkers at the “gaping wound that has been inflicted on this wonderful city – the city that has been such a good and welcoming host to us.” “Above all, we mourn the deaths of so many valiant police officers, fire fighters and other city officials who lost their lives in this tragedy and in the rescue and recovery efforts – people to whom the UN owes a special debt of gratitude for their work to keep us safe over the years,” he said. Today, the Secretary-General sent a message to the UN staff urging them to “help and comfort those colleagues whose loved ones are missing or have been injured.” Recalling that there had been anxiety on Tuesday and Wednesday about possible threats against the UN complex, Mr. Annan sought to reassure the staff and expressed his gratitude to those who had worked despite the tense circumstances. “I want to thank you all for the calm and good humour you have shown, and are showing, in spite of the stress.” “These tragic events make our work to promote peace and relieve suffering all the more important,” he said.