The United States and Israel have sent complaint letters to top United Nations officials contesting their staff's impartiality over the war in the Gaza Strip, documents showed, as hundreds of them protested outside the global organization's European headquarters on Thursday.

U.N. staff carried placards saying "Peace for Gaza" and "Not a Target." They laid over 370 white roses next to a memorial plaque in Geneva to represent each U.N. aid worker killed in the nearly two-year war.

"Today, the U.N. staff are coming together to say that enough is enough, to say that we cannot kill our colleagues in Gaza with such impunity and to say stop to all these murders," Nathalie Meynet, president of the U.N. refugee agency staff council, said at the protest.