UN Secretary General Kofi Annan has said there is an "alarming resurgence" of anti-Semitism in the world.
Annan: "Anti-Semitism is once again rearing its head"
At a first UN conference on anti-Semitism, Mr Annan urged people not to remain silent and tackle the problem.
Nobel laureate and Holocaust survivor Elie Wiesel accused some Muslim nations of using Israel's government policies as a pretext to demonise Jews.
The World Jewish Congress is pushing for a UN General Assembly resolution condemning anti-Semitism.
The body will also ask for a special UN representative to report annually on anti-Semitism, which Jewish groups say is increasing around the world.
"It is hard to believe that, 60 years after the tragedy of the Holocaust, anti-Semitism is once again rearing its head," Mr Annan said at the conference in New York.
Wiesel urged to fight anti-Semitism
"But it is clear that we are witnessing an alarming resurgence of this phenomenon in new forms and manifestations. This time, the world must not - cannot - be silent," he said.
"When we seek justice for the Palestinians - as we must - let us firmly disavow anyone who tries to use that cause to incite hatred against Jews, in Israel or elsewhere."
"There remains a need for constant vigilance," Mr Annan added.
Mr Wiesel - who also addressed the conference's delegates - said that discriminating against Jews often translated into hatred against all minorities and "those who are different".
"When we urge you to fight anti-Semitism, it is because we want to save other people as well," he said.
After the opening speeches, the conference was expected to discuss the role of education, fostering tolerance and other ways of confronting anti-Semitism.
The meeting is the first of a series entitled "Unlearning Intolerance" which brings together voluntary organisations, educational groups and others to look at ways of promoting respect and understanding among communities.
'Worst since Holocaust'
Jewish leaders have accused the UN of neglecting anti-Semitism and of passing a disproportionate number of resolutions against Israel.
"We are seeing the most severe level of anti-Semitism around the globe since the Holocaust," said Elan Steinberg, the executive vice president of the World Jewish Congress.
"The UN has multitudes of annual reports on various racist situations but an obvious neglect of anti-Semitism," he added.
The body, which lobbies to further the interests and needs of Jews and Jewish communities, wants the UN to go beyond a conference and adopt a resolution in the General Assembly on the subject as well as appointing a representative on the subject.
The UN voted in 1947 to create the State of Israel, but in recent decades Israel has regarded the organisation as increasingly hostile.