SAN SALVADOR, Oct 9 (Reuters) - El Salvador will invest some of the $4 million gains it has obtained from its bitcoin operations to build a veterinary hospital, President Nayib Bukele said on Saturday. Bitcoin lost almost 10% of its value on Sept. 9, after the Central American nation became the first worldwide to authorize the cryptocurrency as legal tender. But it has surged more than 30% in the past week to its highest levels since May. The Bitcoin Trust, which Congress authorized in August, with a balance of $150 million, now has a "surplus" of $4 million, Bukele said. "So we decided to invest a part of that money in this: a veterinary hospital for our furry friends," Bukele wrote on Twitter. Bukele said the veterinary hospital would services for basic and emergency care as well as rehabilitation. Reporting by Nelson Renteria; Writing by Stefanie Eschenbacher; Editing by William Mallard Our Standards: The Thomson Reuters Trust Principles.