NEW YORK (Reuters) - UBS AG had trading losses of around $30 million stemming from Facebook Inc's botched initial public offering on Nasdaq OMX Group Inc's U.S. exchange, a source with knowledge of the situation said on Friday. UBS was one of four main market makers involved in Facebook's IPO on May 18. Its losses come on top of claims by Citigroup's market making unit of $20 million, and Knight Capital Group Inc and Citadel Securities of $30 million to $35 million each in losses. (Reporting By John McCrank)