SAN SALVADOR, June 30 (Reuters) - Lawmakers in El Salvador on Wednesday voted to keep the head of the Supreme Court in place for three more years and appointed five new justices, triggering concerns that President Nayib Bukele is shoring up a bid to consolidate power. Bukele"s New Ideas (NI) party and its allies hold a super-majority in El Salvador"s Congress, where lawmakers have now appointed 10 court judges in less than two months. Supreme Court President Oscar Lopez was first appointed last month, just as Bukele"s legislative allies abruptly ousted five judges as well as the attorney general in a move that was harshly criticized by the United States and international rights groups as a dangerous power grab. The new judges to the 15-seat court will be able to serve for nine years. Bukele said lawmakers voted in line with the constitution and selected the judges from candidate lists submitted by bar associations. "Their decisions are totally legitimate and represent the power of the people," Bukele said on Twitter. However, during the congressional session that began on Tuesday and stretched until dawn, lawmaker Dina Argueta from the leftist Farabundo Marti National Liberation Front (FMLN) warned that the new judges were Bukele loyalists whose appointments marked a "concentration of power." Jose Miguel Vivanco, the head of Human Rights Watch in the Americas, also expressed worry that the new judges would not be impartial. "I am concerned about the appointment of judges to be made tonight," he wrote on Twitter shortly before the vote. "Under rule of law, judges must be appointed through a transparent, previously established process that guarantees their independence."