LIMA, June 24 (Reuters) - Peru"s already tense election process was plunged into further disarray after one of the four magistrates on the jury reviewing contested ballots quit after clashing with the other officials over requests to nullify votes. Luis Arce said on Wednesday night he would leave his post after the jury rejected the first 10 requests to annul votes presented by right-wing Keiko Fujimori, who was narrowly behind socialist outsider Pedro Castillo in the June 6 vote. Fujimori has made allegations of fraud with little evidence and sought to disqualify votes in favor of Castillo. Electoral observers have said the vote was carried out cleanly, while the U.S. State Department said it was a "model of democracy." The tight election has starkly divided the copper-rich Andean nation with marches and protests almost daily in the capital Lima. Arce in a resignation letter alleged bias on the jury and said "decisions were already made". His departure could hold up the confirmation of the result as the jury processes the contested ballots with just 44,000 votes between the candidates. The JNE on its Twitter account rejected Arce"s allegation of bias as "offensive" and said a magistrate was not allowed to resign mid-review so he would be suspended instead, and a provisional replacement found "to avoid delaying our work." Castillo"s Free Peru party said on Thursday the resignation was aimed at "preventing the proclamation of Pedro Castillo, thereby ignoring the popular vote, breaking democracy and installing a coup d"état with silk gloves." Fujimori"s conservative Fuerza Popular party has filed hundreds of appeals involving at least 200,000 votes. A lawyer representing Fuerza Popular said that in light of the magistrate´s resignation the government should consider asking the Organization of American States (OAS) to audit the electoral process, as was done in neighbouring Bolivia following contested elections in 2019. In a statement, the OAS said its mission to the country found no fault with the conduct of the election. Castillo, a former reacher and union leader, has rattled Peru"s political elite, mining companies and markets with plans to redistribute mineral wealth and redraft the constitution. He has, however, moderated his rhetoric in recent weeks.